Make BufferSearch less wide (#10459)

This also adds some "responsiveness" so that UI elements are hidden
before everything has to be occluded

Release Notes:

- Improved search UI. It now works in narrower panes, and avoids
scrolling the editor on open.

<img width="899" alt="Screenshot 2024-04-11 at 21 33 17"
src="https://github.com/zed-industries/zed/assets/94272/44b95d4f-08d6-4c40-a175-0e594402ca01">
<img width="508" alt="Screenshot 2024-04-11 at 21 33 45"
src="https://github.com/zed-industries/zed/assets/94272/baf4638d-427b-43e6-ad67-13d43f0f18a2">
<img width="361" alt="Screenshot 2024-04-11 at 21 34 00"
src="https://github.com/zed-industries/zed/assets/94272/ff60b561-2f77-49c0-9df7-e26227fe9225">
<img width="348" alt="Screenshot 2024-04-11 at 21 37 03"
src="https://github.com/zed-industries/zed/assets/94272/a2a700a2-ce99-41bd-bf47-9b14d7082b0e">

crates/editor/src/editor.rs

@@ -471,6 +471,8 @@ pub struct Editor {
                 + Fn(&mut Self, DisplayPoint, &mut ViewContext<Self>) -> Option<View<ui::ContextMenu>>,
         >,
     >,
+    last_bounds: Option<Bounds<Pixels>>,
+    expect_bounds_change: Option<Bounds<Pixels>>,
 }
 
 #[derive(Clone)]
@@ -1485,6 +1487,8 @@ impl Editor {
             inlay_hint_cache: InlayHintCache::new(inlay_hint_settings),
             gutter_hovered: false,
             pixel_position_of_newest_cursor: None,
+            last_bounds: None,
+            expect_bounds_change: None,
             gutter_width: Default::default(),
             style: None,
             show_cursor_names: false,