This reduces the number of multibuffer syncs from 100,000 to 20,000.
Before this change each editor individually observed the project, so
literally any project change was amplified by the number of editors you
had open.
Now editors listen to their buffers instead of the project, and other
users of `cx.observe` on the project have been updated to use specific
events to reduce churn.
Follow up to #26237
Release Notes:
- Improved performance of Zed in large repos with lots of file system
events.
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Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
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