bug#41572: 28.0.50; [PATCH] Support plain project marked with file .emacs-project

[Juri Linkov <juri@linkov.net>]

>> Maybe a better name would be 'project-directory-ignores'
>> with the directory-based backend name 'project-directory'?
>
> I don't know if it's better. What does "directory" mean? Every backend,
> every project has directories.

Then maybe the backend could be named 'project-file'
since a special file defines the project root.

> As mentioned previously, the other option I had considered was 'novc'. Then
> the variable would be called project-novc-ignores.

"novc" is the worst variant.  It's not obvious that it means
"no-version-control", and also will make no sense when more backends
will be added.  Or no more backends are planned, and all other possible
roots should be handled by the same fallback backend?  Or would it be
possible that more backends could be added in project-find-functions
after the file-based fallback backend?  Then the name "fallback"
will make no sense if it will not be the last in project-find-functions.

> This is not a done deal, just what seems the most optimal to me at the
> moment. But opinions welcome.

Maybe it will help to choose a better name while thinking about
more possible backends that could be added later.