UI: improve menu search with dimmed menu prefix

- Show dimmed text for the menu entries leading up to the menu item.
- Show icons between the menu text and menu item.
- Use unicode right pointing triangle instead of arrow.

source/blender/editors/interface/interface_layout.c

@@ -2633,6 +2633,7 @@ void ui_but_add_search(
                            coll_search,
                            ui_rna_collection_search_free_cb,
                            NULL,
+                           NULL,
                            NULL);
   }
   else if (but->type == UI_BTYPE_SEARCH_MENU) {