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/cli/src/cli.rs

@@ -13,6 +13,7 @@ pub enum CliRequest {
     Open {
         paths: Vec<String>,
         urls: Vec<String>,
+        diff_paths: Vec<[String; 2]>,
         wait: bool,
         open_new_workspace: Option<bool>,
         env: Option<HashMap<String, String>>,