Un serialize project search (#2857)

This is the first batch of improvements to current project search. There
are few things we can do better still, but I want to get this out in
next Preview.
Most of the slowness at this point seems to stem from updating UI too
often.

Release Notes:
- Improved project search by making it report results sooner.

---------

Co-authored-by: Julia Risley <julia@zed.dev>