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/project/src/project.rs

@@ -2439,11 +2439,14 @@ impl Project {
         abs_path: impl AsRef<Path>,
         cx: &mut Context<Self>,
     ) -> Task<Result<Entity<Buffer>>> {
-        if let Some((worktree, relative_path)) = self.find_worktree(abs_path.as_ref(), cx) {
-            self.open_buffer((worktree.read(cx).id(), relative_path), cx)
-        } else {
-            Task::ready(Err(anyhow!("no such path")))
-        }
+        let worktree_task = self.find_or_create_worktree(abs_path.as_ref(), false, cx);
+        cx.spawn(async move |this, cx| {
+            let (worktree, relative_path) = worktree_task.await?;
+            this.update(cx, |this, cx| {
+                this.open_buffer((worktree.read(cx).id(), relative_path), cx)
+            })?
+            .await
+        })
     }
 
     #[cfg(any(test, feature = "test-support"))]