Position Grammarly button on top of CM6 editor

GitOrigin-RevId: f96d1897c38e8e14e9247690ee49972a2170f80e

services/web/frontend/stylesheets/app/editor.less

@@ -844,3 +844,7 @@ CodeMirror
     }
   }
 }
+
+grammarly-extension[data-grammarly-shadow-root='true'] {
+  z-index: 1;
+}