Motivation for this is to make things more understandable while figuring
out #20775.
This is intended to be a refactoring that does not affect behavior, but
there are a few tricky spots:
* Previously `File.mtime()` (now `File.disk_state().mtime()`) would
return last known modification time for deleted files. Looking at uses,
I believe this will not affect anything. If there are behavior changes
here I believe they would be improvements.
* `BufferEvent::DirtyChanged` is now only emitted if dirtiness actually
changed, rather than if it may have changed. This should only be an
efficiency improvement.
Release Notes:
- N/A
Co-authored-by: Mikayla Maki <mikayla@zed.dev>
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