We pass all of them to a single editor command, hoping that the editor will be
able to handle multiple files (VS Code and vim do).
We ignore directories that happen to be in the selection range; this makes it
easier to edit multiple files in different folders in tree view. We show an
error if only directories are selected, though.
This helps work around bugs in editors that may get confused about relative
paths (like nvim-remote, see https://github.com/neovim/neovim/issues/18519), and
shouldn't have any negative effect on others.
The "open" command is supposed to behave in the same way as double-clicking a
file in the Finder/Explorer. The concept of jumping to a specific line in the
file doesn't make sense for this; use "edit" instead.
