bug#66317: Project mode-line

[Juri Linkov]

>> Thanks, I've tried this patch on top of Emacs master and it seems to
>> work well.  One small suggestion is to consider giving the project name
>> in the mode line a dedicated face, so people/themes could customize its
>> appearance.  (By default, it could just inherit from `default`.)
>
> Thanks for suggestion, will do on the second round after pushing the
> initial version.

I'm not yet sure whether better to add a new face or a new variable like
grep-hit-face and xref-num-matches-face that refers to the existing face.
Then it would be possible to set such variable e.g. to the face `vc-state-base`
that inherits from `default`.