Improve dropdown menu keyboard navigation (#11491)

* Allow selecting menu items with the space bar in status dropdown menus

* Fix modals opened by keyboard navigation being immediately closed

* Fix menu items triggering modal actions

* Add Tab trapping inside dropdown menu

* Give focus back to last focused element when status dropdown menu closes

app/javascript/mastodon/reducers/modal.js

@@ -10,7 +10,7 @@ export default function modal(state = initialState, action) {
   case MODAL_OPEN:
     return { modalType: action.modalType, modalProps: action.modalProps };
   case MODAL_CLOSE:
-    return initialState;
+    return (action.modalType === undefined || action.modalType === state.modalType) ? initialState : state;
   default:
     return state;
   }