More Git panel refinements (#21928)

- Add and wire through git method stubs
- Organize render methods
- Track modifier changes
- Swap commit buttons when `option`/`alt` is held
- More TODOs

Release Notes:

- N/A

crates/git_ui/src/git_ui.rs

@@ -1,10 +1,21 @@
 use ::settings::Settings;
-use gpui::AppContext;
+use gpui::{actions, AppContext};
 use settings::GitPanelSettings;
 
 pub mod git_panel;
 mod settings;
 
+actions!(
+    git_ui,
+    [
+        StageAll,
+        UnstageAll,
+        DiscardAll,
+        CommitStagedChanges,
+        CommitAllChanges
+    ]
+);
+
 pub fn init(cx: &mut AppContext) {
     GitPanelSettings::register(cx);
 }