bug#70577: [PATCH] New command other-project-prefix

[Dmitry Gutov <dmitry@gutov.dev>]

X-Debbugs-Cc: Juri Linkov <juri@linkov.net>

This is based on Juri's patch in 
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=63648#161, but the idea is 
more focused: to switch the order of events, and first read the full key 
sequence, and then prompt for the project and the command arguments. 
Like we also discussed in the past.

And to try to reuse the even loop in the more natural way. 
Unfortunately, 'C-h' doesn't work here (when called in the middle of the 
sequence) - I'm not sure why. The rest of the behavior seems to work as 
expected.

So this can be a new alternative for the 'C-x p p' binding as well.

Regarding the the use of advice, I didn't find a better way to plug 
(funcall project-prompter) this late. Too complex for pre-command-hook.

Thoughts welcome.