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.

Move things out of SQLBaseStore

This reverts commit 00f0d675.

Its going to get removed soon, so lets not make merge conflicts.

Fix issue #6406 parameter mismatch

Filter state, events_before and events_after in /context requests

Merge branch 'babolivier/context_filters' of github.com:matrix-org/synapse into babolivier/context_filters

Co-Authored-By: Erik Johnston <erik@matrix.org>