We want to wait until we have read the response body before we log the request
as complete, otherwise a confusing thing happens where the request appears to
have completed, but we later fail it.

To do this, we factor the salient details of a request out to a separate
object, which can then keep track of the txn_id, so that it can be logged.

Signed-off-by: Aaron Raimist <aaron@raim.ist>

Signed-off-by: Simon Dwyer <simon@thedwyers.co>

don't filter membership events based on history visibility
as we will already have filtered the messages in the timeline, and state events
are always visible.

and because @erikjohnston said so.

* fix

* changelog

* speed up room summaries by pulling their data from room_memberships rather than room state
* disable LL for incr syncs, and log incr sync stats  (#3840)