Diff view (#32922)

Todo:

* [x] Open diffed files as regular buffers
* [x] Update diff when buffers change
* [x] Show diffed filenames in the tab title
* [x] Investigate why syntax highlighting isn't reliably handled for old
text
* [x] remove unstage/restore buttons

Release Notes:

- Adds `zed --diff A B` to show the diff between the two files

---------

Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>
Co-authored-by: Agus Zubiaga <agus@zed.dev>

crates/buffer_diff/src/buffer_diff.rs

@@ -1028,7 +1028,11 @@ impl BufferDiff {
         let (base_text_changed, mut changed_range) =
             match (state.base_text_exists, new_state.base_text_exists) {
                 (false, false) => (true, None),
-                (true, true) if state.base_text.remote_id() == new_state.base_text.remote_id() => {
+                (true, true)
+                    if state.base_text.remote_id() == new_state.base_text.remote_id()
+                        && state.base_text.syntax_update_count()
+                            == new_state.base_text.syntax_update_count() =>
+                {
                     (false, new_state.compare(&state, buffer))
                 }
                 _ => (true, Some(text::Anchor::MIN..text::Anchor::MAX)),