bug#41890: bug#42210: bug#41890: 28.0.50; [PATCH]: Add bindings for project.el

[Juri Linkov]

> How about having a project-other-window-commands defcustom for C-x 4 p,
> and using the entirety of project-prefix-map for C-x 5 p and C-x t t?
> C-x 4 p can prompt as per my patch, and C-x 5 p and C-x t t could just
> put a static message in the minibuffer like other-frame-prefix and
> other-tab-prefix do at present.

Currently there are separate key sequences ‘C-x p’ and ‘C-x p p’
followed by almost the same list of possibles suffixes, where e.g.
‘C-x p f’ visits a file of the current project, whereas ‘C-x p p f’
prompts for another project and visits its file.

Should the same distinction be preserved in other-place commands?
Then ‘C-x 4 p f’ will visit a file of the current project in another
window, whereas ‘C-x 4 p p f’ will prompt for another project and visit
its file in another window.  The same distinction could apply also to
‘C-x 5 p f’ / ‘C-x 5 p p f’ and ‘C-x t p f’ / ‘C-x t p p f’.