Previously, we just had very basic partial room exclusion based on
whether we were lazy-loading room members. Now with this PR, we added
`must_await_full_state(...)` with rules to check if we have a we're only
requesting `required_state` which is completely satisfied even with
partial state.
Partially-stated rooms should have all state events except for remote
membership events so if we require a remote membership event anywhere,
then we need to return `True`.
This triggers the client to start a new sliding sync connection. If we
don't do this and the client asks for the full range of rooms, we end up
sending down all rooms and their state from scratch (which can be very
slow)
This causes things like
https://github.com/element-hq/element-x-ios/issues/3115 after we restart
the server
---------
Co-authored-by: Eric Eastwood <eric.eastwood@beta.gouv.fr>
