Deprecate modus-themes-region; use overrides

This is the last user option that we need to deprecate for the release
of version 4.  Now all colour-related changes happen through palette
overrides.

Thanks to Christian Tietze for reminding me about it:
<https://lists.sr.ht/~protesilaos/modus-themes/%3Cm1ilhtrs09.fsf%40christiantietze.de%3E>.

doc/modus-themes.org

@@ -307,8 +307,7 @@ This is how a basic setup could look like:
 
 ;; Add all your customizations prior to loading the themes.
 (setq modus-themes-italic-constructs t
-      modus-themes-bold-constructs nil
+      modus-themes-bold-constructs nil)
-      modus-themes-region '(bg-only no-extend))
 
 ;; Load the theme of your choice.
 (load-theme 'modus-operandi)
@@ -325,8 +324,7 @@ This is how a basic setup could look like:
 
 ;; Add all your customizations prior to loading the themes
 (setq modus-themes-italic-constructs t
-      modus-themes-bold-constructs nil
+      modus-themes-bold-constructs nil)
-      modus-themes-region '(bg-only no-extend))
 
 ;; Load the theme of your choice.
 (load-theme 'modus-operandi :no-confim)
@@ -355,8 +353,7 @@ package configurations in their setup.  We use this as an example:
   :init
   ;; Add all your customizations prior to loading the themes
   (setq modus-themes-italic-constructs t
-        modus-themes-bold-constructs nil
+        modus-themes-bold-constructs nil)
-        modus-themes-region '(bg-only no-extend))
   :config
   ;; Load the theme of your choice.
   (load-theme 'modus-operandi)
@@ -370,8 +367,7 @@ package configurations in their setup.  We use this as an example:
   :init
   ;; Add all your customizations prior to loading the themes
   (setq modus-themes-italic-constructs t
-        modus-themes-bold-constructs nil
+        modus-themes-bold-constructs nil)
-        modus-themes-region '(bg-only no-extend))
   :config
   ;; Load the theme of your choice.
   (load-theme 'modus-operandi :no-confim)
@@ -384,8 +380,7 @@ The same without ~use-package~:
 ;;; For the built-in themes which cannot use `require':
 ;; Add all your customizations prior to loading the themes
 (setq modus-themes-italic-constructs t
-      modus-themes-bold-constructs nil
+      modus-themes-bold-constructs nil)
-      modus-themes-region '(bg-only no-extend))
 
 ;; Load the theme of your choice:
 (load-theme 'modus-operandi) ;; OR (load-theme 'modus-vivendi)
@@ -399,8 +394,7 @@ The same without ~use-package~:
 
 ;; Add all your customizations prior to loading the themes
 (setq modus-themes-italic-constructs t
-      modus-themes-bold-constructs nil
+      modus-themes-bold-constructs nil)
-      modus-themes-region '(bg-only no-extend))
 
 ;; Load the theme of your choice:
 (load-theme 'modus-operandi :no-confim) ;; OR (load-theme 'modus-vivendi :no-confim)
@@ -506,11 +500,6 @@ reloaded for changes to take effect.
       '((matches . (extrabold))
         (selection . (semibold italic text-also)))
 
-      ;; Options for `modus-themes-region' are either nil (the default),
-      ;; or a list of properties that may include any of those symbols:
-      ;; `no-extend', `bg-only'.
-      modus-themes-region '(bg-only no-extend)
-
       modus-themes-org-blocks 'gray-background ; {nil,'gray-background,'tinted-background}
 
       ;; The `modus-themes-headings' is an alist: read the manual's
@@ -792,54 +781,6 @@ Is the same as:
 
 [[#h:d959f789-0517-4636-8780-18123f936f91][Make completion matches more or less colorful]].
 
-** Option for active region
-:properties:
-:alt_title: Active region
-:description: Choose between various styles for the active region
-:custom_id: h:60798063-b4ad-45ea-b9a7-ff7b5c0ab74c
-:end:
-#+vindex: modus-themes-region
-
-[ Simplified as part of {{{development-version}}}.  It no longer
-  accepts an =accented= symbol.  Changes to colors can be implemented
-  via the overrides. ]
-
-Brief: Control the style of the region.
-
-Symbol: ~modus-themes-region~ (=choice= type, list of properties)
-
-Possible values are expressed as a list of properties (default is ~nil~ or
-an empty list).  The list can include any of the following symbols:
-
-+ ~no-extend~
-+ ~bg-only~
-
-The default (a ~nil~ value or an empty list) is a prominent gray
-background that overrides all foreground colors in the area it
-encompasses.  Its reach extends to the edge of the window.
-
-The ~no-extend~ property limits the region to the end of the line, so that
-it does not reach the edge of the window.
-
-The ~bg-only~ property makes the region's background color more subtle to
-allow the underlying text to retain its foreground colors.
-
-Combinations of any of those properties are expressed as a list, like in
-these examples:
-
-#+begin_src emacs-lisp
-(no-extend)
-(bg-only no-extend)
-#+end_src
-
-The order in which the properties are set is not significant.
-
-In user configuration files the form may look like this:
-
-#+begin_src emacs-lisp
-(setq modus-themes-region '(bg-only no-extend))
-#+end_src
-
 ** Option for org-mode block styles
 :properties:
 :alt_title: Org mode blocks

modus-operandi-deuteranopia-theme.el

@@ -158,8 +158,8 @@ standard).")
       (bg-hover            "#97dfed")
       (bg-hover-secondary  "#f5d0a0")
       (bg-hl-line          "#d0d6ec")
-      (bg-region           "#bcbcbc")
+      (bg-region           "#bdbdbd")
-      (bg-region-subtle    "#f0e0cc")
+      (fg-region           "#000000")
 
       (bg-char-0 "#7feaff")
       (bg-char-1 "#ffaaff")

modus-operandi-theme.el

@@ -156,8 +156,8 @@ which corresponds to a minimum contrast in relative luminance of
       (bg-hover            "#94d4ff")
       (bg-hover-secondary  "#f5d0a0")
       (bg-hl-line          "#d0d6ec")
-      (bg-region           "#bcbcbc")
+      (bg-region           "#bdbdbd")
-      (bg-region-subtle    "#f0e0cc")
+      (fg-region           "#000000")
 
       (bg-char-0 "#7feaff")
       (bg-char-1 "#ffaaff")

modus-operandi-tinted-theme.el

@@ -156,7 +156,7 @@ which corresponds to a minimum contrast in relative luminance of
       (bg-hover-secondary  "#f5d0a0")
       (bg-hl-line          "#f1d5d0")
       (bg-region           "#c2bcb5")
-      (bg-region-subtle    "#d9f2c0")
+      (fg-region           "#000000")
 
       (bg-char-0 "#7feaff")
       (bg-char-1 "#ffaaff")

modus-themes.el

@@ -732,43 +732,7 @@ In user configuration files the form may look like this:
 (make-obsolete-variable 'modus-themes-paren-match nil "4.0.0")
 (make-obsolete-variable 'modus-themes-syntax nil "4.0.0")
 (make-obsolete-variable 'modus-themes-links nil "4.0.0")
-
+(make-obsolete-variable 'modus-themes-region nil "4.0.0")
-(defcustom modus-themes-region nil
-  "Control the overall style of the active region.
-
-The value is a list of properties, each designated by a symbol.
-The default (a nil value or an empty list) is a prominent gray
-background that overrides all foreground colors in the area it
-encompasses.  Its reach extends to the edge of the window.
-
-The `no-extend' property limits the region to the end of the
-line, so that it does not reach the edge of the window.
-
-The `bg-only' property makes the region's background color more
-subtle to allow the underlying text to retain its foreground
-colors.
-
-Combinations of properties are expressed as a list, like in these
-examples:
-
-    (no-extend)
-    (bg-only no-extend)
-
-The order in which the properties are set is not significant.
-
-In user configuration files the form may look like this:
-
-    (setq modus-themes-region (quote (bg-only no-extend)))"
-  :group 'modus-themes
-  :package-version '(modus-themes . "4.0.0")
-  :version "30.1"
-  :type '(set :tag "Properties" :greedy t
-              (const :tag "Do not extend to the edge of the window" no-extend)
-              (const :tag "Background only (preserve underlying colors)" bg-only))
-  :set #'modus-themes--set-option
-  :initialize #'custom-initialize-default
-  :link '(info-link "(modus-themes) Active region"))
-
 (make-obsolete-variable 'modus-themes-deuteranopia nil "4.0.0")
 (make-obsolete-variable 'modus-themes-mail-citations nil "4.0.0")
 (make-obsolete-variable 'modus-themes-tabs-accented nil "4.0.0")
@@ -1409,20 +1373,6 @@ FG and BG are the main colors."
      :weight
      (if (and weight (null bold)) weight 'unspecified))))
 
-(defun modus-themes--region (bg fg bgsubtle)
-  "Apply `modus-themes-region' styles.
-
-BG and FG are the main values that are used by default.  BGSUBTLE
-is a less intense variant of BG."
-  (let* ((properties (modus-themes--list-or-warn 'modus-themes-region))
-         (bg-only (memq 'bg-only properties)))
-    (list :background
-          (if bg-only bgsubtle bg)
-          :foreground
-          (if bg-only 'unspecified fg)
-          :extend
-          (if (memq 'no-extend properties) nil t))))
-
 
 
 ;;;; Face specifications
@@ -1563,7 +1513,7 @@ is a less intense variant of BG."
     `(pgtk-im-0 ((,c :inherit modus-themes-intense-cyan)))
     `(read-multiple-choice-face ((,c :inherit (bold modus-themes-mark-alt))))
     `(rectangle-preview ((,c :inherit secondary-selection)))
-    `(region ((,c ,@(modus-themes--region bg-region fg-main bg-region-subtle))))
+    `(region ((,c :background ,bg-region :foreground ,fg-region)))
     `(secondary-selection ((,c :background ,bg-hover-secondary)))
     `(separator-line ((,c :underline ,bg-active)))
     `(shadow ((,c :foreground ,fg-dim)))

modus-vivendi-deuteranopia-theme.el

@@ -157,8 +157,8 @@ standard).")
       (bg-hover            "#004f70")
       (bg-hover-secondary  "#654a39")
       (bg-hl-line          "#2f3849")
-      (bg-region           "#5c5c5c")
+      (bg-region           "#5a5a5a")
-      (bg-region-subtle    "#4f1c2f")
+      (fg-region           "#ffffff")
 
       (bg-char-0 "#0050af")
       (bg-char-1 "#7f1f7f")

modus-vivendi-theme.el

@@ -155,8 +155,8 @@ which corresponds to a minimum contrast in relative luminance of
       (bg-hover            "#004f70")
       (bg-hover-secondary  "#654a39")
       (bg-hl-line          "#2f3849")
-      (bg-region           "#5c5c5c")
+      (bg-region           "#5a5a5a")
-      (bg-region-subtle    "#4f1c2f")
+      (fg-region           "#ffffff")
 
       (bg-char-0 "#0050af")
       (bg-char-1 "#7f1f7f")

modus-vivendi-tinted-theme.el

@@ -150,7 +150,7 @@ which corresponds to a minimum contrast in relative luminance of
       (bg-hover-secondary  "#654a39")
       (bg-hl-line          "#303a6f")
       (bg-region           "#555a66")
-      (bg-region-subtle    "#0f4f30")
+      (fg-region           "#ffffff")
 
       (bg-char-0 "#0050af")
       (bg-char-1 "#7f1f7f")