bug#33870: 27.0.50; xref-goto-xref not configurable

[martin rudalics]

> display-buffer--maybe-at-bottom can be renamed to
> display-buffer-maybe-at-bottom without a deprecation alias
> because it was added in Emacs 27.

The 'display-buffer--maybe-' functions are macros in disguise invented
by Chong to simplify coding the rest.  Unless we can't avoid it, I
would not make them public because then we would have to (1) document
them, (2) explain the semantics of the "maybe" and (3) justify why the
remaining 'display-buffer--maybe-' functions are not public.

Also note that 'display-buffer' resizes a window iff that window is
new or always has shown the buffer to display before.

There's one thing about 'display-buffer-at-bottom' that stupefies me:
Here

             (let (split-width-threshold)
               (setq window (window--try-to-split-window bottom-window alist)))

we bind ‘split-width-threshold’ so we can split the bottom window into
two side by side windows.  I recently found a branch of mine where I
bind 'split-height-threshold' to nil instead and now cannot remember
what we really wanted - split that window horizontally or vertically.
Can you?  In either case feel free to change that to what you consider
the more appropriate binding - maybe even binding both.

Thanks, martin