bug#57807: 29.0.50; Make vc-print-branch-log able to log multiple branches

[Juri Linkov <juri@linkov.net>]

>> After you will push it, it would be good also to try to generalize it
>> to other vc commands.  The problem is that some commands already use
>> C-u for other purposes, such as 'C-u C-x v L' asks for a limit.  What
>> would be a possible way to set vc-want-edit-command-p without using a
>> prefix arg?  Maybe to add a new command that will only set
>> vc-want-edit-command-p for the next vc command, and bind it to
>> e.g. 'C-x v c'.  Then 'C-x v c C-x v L' will allow editing the root
>> log command.
>
> Right.  It would be good to find a way to make all this consistent.
> It's unfortunate that C-x v l and C-x v P were different to begin with.
>
> Regarding your idea, how about 'C-x V V'?  It's easier to type, won't
> clash with another command we might want to put on 'c', and feels a bit
> like C-x 4 4, C-x 5 5 etc.

It's easier to type the same letter again, but holding the Shift key
for V V after typing Control-X is more hard to type in a key sequence
'C-x V V C-x v L'.  It's a pity that 'C-x v v' is not available.

> Though, to be honest, I'd prefer it if we could come up with something
> involving multiple 'C-u'.

Another variant is to bind 'C-x v c' to a command that uses
'read-key-sequence' to read a key sequence from the vc keymap,
then call a command with call-interactively while let-binding
vc-want-edit-command-p, like project--switch-project-command does.
Then e.g. 'C-x v c L' will have mnemonic "vc command for root log".