bug#66317: Project mode-line

[Juri Linkov]

There is another problem: calling 'project-name' while evaluating
'mode-line-format' often changes the coding system mode-line indicator
from U (utf-8) to raw-text during saving the current buffer.

Here is a backtrace:

- project-name
- project--value-in-dir (that uses with-temp-buffer)
- hack-dir-local-variables-non-file-buffer
- hack-local-variables-apply

Then in the last function the coding system is broken
in two different ways:

1. by 'hack-one-local-variable' in `emacs -Q`
2. by (run-hooks 'hack-local-variables-hook)
   in buffers where flyspell-mode is enabled
   'flyspell-hack-local-variables-hook' breaks
   the coding system too.