Do not send first missing file event as well, Do not close typing installers watches just to recreate them

[sheetalkamat]

Handling as per #22496 (comment)

Fixes #22581

[sheetalkamat]

@amcasey can you please take a look. Thanks

[amcasey]

The missing file event part looks correct. I haven't had a chance to read the TI bit yet.

[RyanCavanaugh]

What was the root cause of the bug? The code looks correct but the important behavioral difference between it and the old version isn't obvious.

[sheetalkamat]

There were two causes
1: The delete event was sent on first invoke from the fileWatcher of missing files. (which we shouldnt)
2. Whenever the files are invalidated, we close all existing watches and create new watches which is expensive.. (it would be same list of files) which is what happens without the fix (since deleted is sent on first poll, invalidating the project, resulting in creating new install request which closes existing watch and sets new watcher which again sends file deleted event)

[sheetalkamat]

@RyanCavanaugh does that answer your question, Is it ready to merge. I would like to get this in tonights nightly. Thanks