Overhaul search bar layout

* Use a single row, instead of centering the search bar within a double-row toolbar.
* Search query controls on the left, navigation on the right
* Semantic is the final mode, for greater stability between buffer and project search.
* Prevent query editor from moving when toggling path filters

crates/theme/src/theme.rs

@@ -437,11 +437,11 @@ pub struct Search {
     pub match_index: ContainedText,
     pub major_results_status: TextStyle,
     pub minor_results_status: TextStyle,
-    pub dismiss_button: Interactive<IconButton>,
     pub editor_icon: IconStyle,
     pub mode_button: Toggleable<Interactive<ContainedText>>,
     pub nav_button: Toggleable<Interactive<ContainedLabel>>,
     pub search_bar_row_height: f32,
+    pub search_row_spacing: f32,
     pub option_button_height: f32,
     pub modes_container: ContainerStyle,
 }