Finish removing git repository state and scanning logic from worktrees (#27568)

This PR completes the process of moving git repository state storage and
scanning logic from the worktree crate to `project::git_store`.

Release Notes:

- N/A

---------

Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
Co-authored-by: Conrad <conrad@zed.dev>

crates/multi_buffer/src/multi_buffer.rs

@@ -2475,6 +2475,7 @@ impl MultiBuffer {
         let buffer_id = diff.buffer_id;
         let buffers = self.buffers.borrow();
         let Some(buffer_state) = buffers.get(&buffer_id) else {
+            eprintln!("no buffer");
             return;
         };