Update docker runtime image to Alpine v3.11

Make get_e2e_cross_signing_key delegate to get_e2e_cross_signing_keys_bulk

... mostly because the latter has a cache.

There's no point carefully dividing a list into batches, and then completely
ignoring the batches.

use an upsert to update device_lists_outbound_last_success

most of these params don't really need to be lists.

Speed up fetching device lists changes in sync.

Fix lost events on replication reconnection

... otherwise we can believe we're up to date when we're not.

Currently we copy `users_who_share_room` needlessly about three times,
which is expensive when the set is large (which it can easily be).

We're pretty close to having mypy working for `synapse.federation`, so let's
finish the job.

This caused `prev_state_ids` to be incorrect if the state event was not
replacing an existing state entry.

looks like we managed to break this during the refactorathon.

This will be used to coordinate stream IDs across multiple writers.

Functions as the equivalent of both `StreamIdGenerator` and
`SlavedIdTracker`.

Fix MANIFEST.in

An update of check-manifest shone some light on some issues with MANIFEST.in, specifically that we didn't ignore/prune the contrib directory, and that we were using prune instead of exclude for files. This fixes both issues.

Fixes #7403

We forgot to set the password on the subscriber connection, as well as
not calling super methods for overridden connectionMade/connectionLost
functions.