This covers the "recents" section and rough design exclusively. It is known that the Field does nothing and that there's a bunch of missing functionality - this is to be iterated upon in future PRs. Labs flag is to aide development and should be removed in a very near future PR.
Also, this is focusing on DMs and not user lists in general because I misinterpreted the scope. I'll fix this in a future PR and instead make this the best DM invite dialog it can be.
Closes https://github.com/vector-im/riot-web/issues/11197
