Update roomlist when an event is decrypted

[dbkr]

Events are now decrypted asynchronously, so are not decrypted
at the time of the Room.timeline which is when our RoomList
got the chance to update. It needs to update once the event has
been decrypted.

Ideally we would not update the whole room list order, but this is
how all the room list re-ordering happens right now, so staying
consistent with this.

Fixes element-hq/element-web#5020

[ara4n]

this feels dangerous. are you sure this isn't going to fire in a tight loop when decrypting initialSyncs?

[ara4n]

although i guess the fact the update is delayed stops it from exploding... and presumably there isn't actually a better solution.

lgtm then.

[dbkr]

I think we will get one of these for every event decrypted when, for example, we get a key from a different device as a result of a key request, but the updates are rate-limited so are designed to handle being called in a tight loop (as they are in other situations, eg. when a bunch of events arrive on the end of the timeline from a catchup sync). This is basically just how the js-sdk works (ie. doesn't do event batching)

[ara4n]

lgtm.