bug#42210: Add -other-window variants of project-prefix-map commands

[Juri Linkov]

> Here is a patch implementing commands under C-x 4 p.  If the approach is
> thought sound I can also prepare patches for C-x 5 p and C-x t p.
>
> I have tested the attached change except for the autoload cookies which
> I am not sure will work with my new macro.  And I'm not sure I should be
> doing this with a macro instead of a function which calls fset -- please
> advise.

Thanks for the patch.  On emacs-devel you said that rather than add
definitions of project-find-file-other-window, etc.
display-buffer-override-next-command could be used.  But there is no
display-buffer-override-next-command in your patch, and definitions of
project-find-file-other-window etc. are still added (with the help of macro).

Would it be possible to define the 'C-x 4 p' map the same way as
'C-x p p' is defined?  There is a patch in https://debbugs.gnu.org/41890#127
to use the default project keymap 'C-x p' in 'C-x p p'.  You could try to
use the same keymap in 'C-x 4 p', and wrap the command call with
display-buffer-override-next-command.