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/zed/src/zed.rs

@@ -570,7 +570,10 @@ fn register_actions(
             window.toggle_fullscreen();
         })
         .register_action(|_, action: &OpenZedUrl, _, cx| {
-            OpenListener::global(cx).open_urls(vec![action.url.clone()])
+            OpenListener::global(cx).open(RawOpenRequest {
+                urls: vec![action.url.clone()],
+                ..Default::default()
+            })
         })
         .register_action(|_, action: &OpenBrowser, _window, cx| cx.open_url(&action.url))
         .register_action(|workspace, _: &workspace::Open, window, cx| {