commit view: Fix layout shift while loading commit (#44548)

Fixes a few cases where the commit view would layout shift as the diff
loaded. This was caused by:
- Adding the commit message buffer after all the diff files
- Using the gutter dimensions from the last frame for the avatar spacing

Release Notes:

- commit view: Fix layout shift while loading commit

---------

Co-authored-by: MrSubidubi <dev@bahn.sh>

crates/vim/src/normal/scroll.rs

@@ -294,11 +294,10 @@ mod test {
     async fn test_scroll(cx: &mut gpui::TestAppContext) {
         let mut cx = VimTestContext::new(cx, true).await;
 
-        let (line_height, visible_line_count) = cx.editor(|editor, window, _cx| {
+        let (line_height, visible_line_count) = cx.update_editor(|editor, window, cx| {
             (
                 editor
-                    .style()
-                    .unwrap()
+                    .style(cx)
                     .text
                     .line_height_in_pixels(window.rem_size()),
                 editor.visible_line_count().unwrap(),

crates/vim/src/test.rs

@@ -2399,7 +2399,7 @@ async fn test_clipping_on_mode_change(cx: &mut gpui::TestAppContext) {
             .end;
         editor.last_bounds().unwrap().origin
             + editor
-                .display_to_pixel_point(current_head, &snapshot, window)
+                .display_to_pixel_point(current_head, &snapshot, window, cx)
                 .unwrap()
     });
     pixel_position.x += px(100.);

crates/vim/src/test/neovim_backed_test_context.rs

@@ -304,11 +304,10 @@ impl NeovimBackedTestContext {
         self.neovim.set_option(&format!("scrolloff={}", 3)).await;
         // +2 to account for the vim command UI at the bottom.
         self.neovim.set_option(&format!("lines={}", rows + 2)).await;
-        let (line_height, visible_line_count) = self.editor(|editor, window, _cx| {
+        let (line_height, visible_line_count) = self.update_editor(|editor, window, cx| {
             (
                 editor
-                    .style()
-                    .unwrap()
+                    .style(cx)
                     .text
                     .line_height_in_pixels(window.rem_size()),
                 editor.visible_line_count().unwrap(),