Fix c-ts-mode bsd-style indentation of union bodies (bug#81255)

* lisp/progmodes/c-ts-mode.el (c-ts-mode--simple-indent-rules): Add
"union_specifier" to the parent-is regexp.

* test/lisp/progmodes/c-ts-mode-resources/indent-bsd.erts: New test.

lisp/progmodes/c-ts-mode.el

@@ -501,6 +501,7 @@ MODE can be `c' or `cpp'.  STYLE can be `gnu', `k&r', `linux', `bsd'."
            ((parent-is ,(rx (or "function_definition"
                                 "struct_specifier"
                                 "enum_specifier"
+                                "union_specifier"
                                 "function_declarator"
                                 "template_declaration")))
             standalone-parent 0)

test/lisp/progmodes/c-ts-mode-resources/indent-bsd.erts

@@ -125,3 +125,12 @@ if (true)
 else
         break;
 =-=-=
+
+Name: Union (bug#81255)
+
+=-=
+union u
+{
+        int i;
+};
+=-=-=