bug#35385: 27.0.50; Make dired-dwim-target aware of other frames

[Juri Linkov]

> I wished this could be made configurable somehow.  FWIW I liked the
> former behavior more so I :override advice
> `dired-dwim-target-directories'.  It would be good if the used function
> would at least be bound to a new defvar.  A defcustom with some
> reasonable choices would probably be even better (old behavior + new
> behavior would already be a good start).

The idea to use the recent buffer was borrowed from compare-windows
that for backward-compatibility has such defcustom:

  (defcustom compare-windows-get-window-function
    'compare-windows-get-recent-window
    "Function that provides the window to compare with."
    :type '(choice
            (function-item :tag "Most recently used window"
                           compare-windows-get-recent-window)
            (function-item :tag "Next window"
                           compare-windows-get-next-window)
            (function :tag "Your function"))
    :group 'compare-windows
    :version "25.1")

So dired-dwim-target could have a similar defcustom
with choices for recent/next window.