Follow-up of https://github.com/zed-industries/zed/pull/24307
Brings back the PR and fixes the issue with the git status not
propagated, if computed too slow.
Now, git repo update
* waits in the background for all `scan_dir` repo status updates and
triggers another status update send afterwards
* ensures that the update sent is reported correctly (`scanning = true`)
if either FS or status scan is running still
* during worktree's git statuses updates, bumps `status_scan_id` to
ensure the repo update is reported to all subscribers
Release Notes:
- Improved project panel's speed in large projects
744579ede9