bug#39035: Show key bindings on M-x completion

[Stefan Kangas]

Severity: wishlist

In the completion interface for M-x, please add functionality to show
the key bindings in parenthesis after the command.  This functionality
is already there in the highly popular helm and swiper completion
frameworks, which could be useful for reference.

For example, when typing M-x kmacro TAB, one should see:

   kmacro-insert-counter (C-x C-k TAB)
   kmacro-set-counter (C-x C-k C-c)
   [...]

Ideally, the keybinding should also use a different color from the command.

This was discussed on emacs-devel, and Stefan Monnier suggested that
it shouldn't be too hard to do:
https://lists.gnu.org/archive/html/emacs-devel/2020-01/msg00115.html

Best regards,
Stefan Kangas