Add a progress indicator while scanning files?

[TysonAndre]

In a project with many files (and 1 scan thread(process)), there is a long time between scanning and analyzing

Scanning files...
(10 seconds later) Analyzing files...

It might help to show some indication psalm is actively scanning.

(e.g. show a single character with a spinner / - \ |, rate limited to once per 0.x times per second, at the time when a new file gets scanned)

Then overwrite the character with Analyzing files...

Estimating the percentage process and showing a progress bar may also be possible (e.g. cache the total number of files that were scanned last run in the cache dir)

[weirdan]

Implemented in #10345