Back out cross-signing code added in Synapse 1.5.0, which caused a performance regression.

Pass in Database object to data stores.

Pull out room_invite_state_types config option once.

Co-Authored-By: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

`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>