Git improvements (#24238)

- **Base diffs on uncommitted changes**
- **Show added files in project diff view**
- **Fix git panel optimism**

Release Notes:

- Git: update diffs to be relative to HEAD instead of the index; to pave
the way for showing which hunks are staged

---------

Co-authored-by: Cole <cole@zed.dev>

crates/editor/src/editor.rs

@@ -1285,7 +1285,7 @@ impl Editor {
 
         let mut code_action_providers = Vec::new();
         if let Some(project) = project.clone() {
-            get_unstaged_changes_for_buffers(
+            get_uncommitted_changes_for_buffer(
                 &project,
                 buffer.read(cx).all_buffers(),
                 buffer.clone(),
@@ -13657,7 +13657,7 @@ impl Editor {
                 let buffer_id = buffer.read(cx).remote_id();
                 if self.buffer.read(cx).change_set_for(buffer_id).is_none() {
                     if let Some(project) = &self.project {
-                        get_unstaged_changes_for_buffers(
+                        get_uncommitted_changes_for_buffer(
                             project,
                             [buffer.clone()],
                             self.buffer.clone(),
@@ -14413,7 +14413,7 @@ impl Editor {
     }
 }
 
-fn get_unstaged_changes_for_buffers(
+fn get_uncommitted_changes_for_buffer(
     project: &Entity<Project>,
     buffers: impl IntoIterator<Item = Entity<Buffer>>,
     buffer: Entity<MultiBuffer>,
@@ -14422,7 +14422,7 @@ fn get_unstaged_changes_for_buffers(
     let mut tasks = Vec::new();
     project.update(cx, |project, cx| {
         for buffer in buffers {
-            tasks.push(project.open_unstaged_changes(buffer.clone(), cx))
+            tasks.push(project.open_uncommitted_changes(buffer.clone(), cx))
         }
     });
     cx.spawn(|mut cx| async move {