feat(ui): Room List should have a new sorter to put room with local event to the top

[Hywan]

We want the room list to have a new sorter that puts all rooms with a local event/local echoes to the top of the list.

Technical challenge — A Room doesn't have a pointer to a RoomSendQueue, so it's not possible to connect the two in a room list sorter, at least not in a clean way. However, in https://github.com/matrix-org/matrix-rust-sdk/issues/4112, we will store the LatestEvent in the RoomInfo for caching purposes. (This mechanism will already trigger a RoomList update.) We may abuse this to store a special information indicating it's a local event, and thus we will be able to implement such sorter.

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• Discussion https://github.com/element-hq/customer-success/issues/366#issuecomment-2758344046