Project Diff 2 (#23891)

This adds a new version of the project diff editor to go alongside the
new git panel.

The basics seem to be working, but still todo:

* [ ] Fix untracked files
* [ ] Fix deleted files
* [ ] Show commit message editor at top
* [x] Handle empty state
* [x] Fix panic where locator sometimes seeks to wrong excerpt

Release Notes:

- N/A

crates/editor/src/inlay_hint_cache.rs

@@ -743,12 +743,12 @@ fn determine_query_ranges(
     excerpt_visible_range: Range<usize>,
     cx: &mut Context<'_, MultiBuffer>,
 ) -> Option<QueryRanges> {
+    let buffer = excerpt_buffer.read(cx);
     let full_excerpt_range = multi_buffer
-        .excerpts_for_buffer(excerpt_buffer, cx)
+        .excerpts_for_buffer(buffer.remote_id(), cx)
         .into_iter()
         .find(|(id, _)| id == &excerpt_id)
         .map(|(_, range)| range.context)?;
-    let buffer = excerpt_buffer.read(cx);
     let snapshot = buffer.snapshot();
     let excerpt_visible_len = excerpt_visible_range.end - excerpt_visible_range.start;