Pull out room_invite_state_types config option once.

`Measure` incorrectly assumed that it was the only thing being done by the parent `LoggingContext`. For instance, during a "renew group attestations" operation, hundreds of `outbound_request` calls could take place in parallel, all using the same `LoggingContext`. This would mean that any resources used during *any* of those calls would be reported against *all* of them, producing wildly inaccurate results.

Instead, we now give each `Measure` block its own `LoggingContext` (using the parent `LoggingContext` mechanism to ensure that the log lines look correct and that the metrics are ultimately propogated to the top level for reporting against requests/backgrond tasks).

Pulling things out of config is currently surprisingly expensive.

This API was added way back in 0.17.0; the code here is annoying to maintain
and entirely redundant.

Port SyncHandler to async/await

Create a Database class and move methods out of SQLBaseStore

Port rest client v2_alpha to async/await

Port rest/v1 to async/await

This reverts commit dc874789.

Signed-off-by: Clifford Garwood II <cliff@cigii.com>

replace the event_info dict with an attrs thing

Signed-off-by: Clifford Garwood II <cliff@cigii.com>

Clean up SQLBaseStore private function usage

Make synapse_port_db exit with a non-0 code if something failed

have_events was a map from event_id to rejection reason (or None) for events
which are in our local database. It was used as filter on the list of
event_ids being passed into get_events_as_list. However, since
get_events_as_list will ignore any event_ids that are unknown or rejected, we
can equivalently just leave it to get_events_as_list to do the filtering.

That means that we don't have to keep `have_events` up-to-date, and can use
`have_seen_events` instead of `get_seen_events_with_rejection` in the one place
we do need it.