Add loading state to the new room list view (#29725)

* add loading state to view model and spinner to room list vieqw

* Update snapshots and add loading test

* avoid nested ternary operator

* Add room list skeleton loading state

* Fix loading logic

- Create RoomListStoreV3Event as to not conflict with loading event definition in Create RoomListStoreEvent.
- Add a loaded event
- Use it to determine loaded state in useFilteredRooms rather than the update event which gets fired in other cases.

* Fix isLoadingRooms logic

* update snapshots and fix test

* Forcing an empty commit to fix PR

* Fix _components.pcss order

* Fix test that wasn't doing anything

* fix tests

res/css/views/rooms/_RoomSublist.pcss

@@ -404,8 +404,7 @@ Please see LICENSE files in the repository root for full details.
     height: 240px;
 
     &::before {
-        background: $roomsublist-skeleton-ui-bg;
-
+        background-color: var(--cpd-color-bg-subtle-secondary);
         width: 100%;
         height: 100%;