Support vim-mode in git commit editor (#33222)

Release Notes:

- Added support for vim-mode on git commit editor (modal included)

Side notes: 
- Maybe in the future (or even on this PR) a config could be added to
let the user choose whether to enable vim-mode on this editor or not?
And on the agent message editor as well.

crates/git_ui/src/git_panel.rs

@@ -388,6 +388,7 @@ pub(crate) fn commit_message_editor(
     commit_editor.set_collaboration_hub(Box::new(project));
     commit_editor.set_use_autoclose(false);
     commit_editor.set_show_gutter(false, cx);
+    commit_editor.set_use_modal_editing(true);
     commit_editor.set_show_wrap_guides(false, cx);
     commit_editor.set_show_indent_guides(false, cx);
     let placeholder = placeholder.unwrap_or("Enter commit message".into());