Fixes https://github.com/vector-im/riot-web/issues/14475
Background: Sticky rooms are actually a pair of lies to the underlying algorithm as a combination of REMOVE_ROOM/NEW_ROOM calls so they don't get considered as needing to be sorted. When a room is added under the importance algorithm, it is expected that the category it is being added to will be re-sorted to account for the change, however we weren't doing that since we optimized the NewRoom path to be a splice operation.
Travis Ralston
6a38833a2b