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>

make cross signing signature index non-unique

Ensure that the the default settings for the room directory are that the it is hidden from public view by default. 

(hopefully)

... and deobfuscate the relevant bit of code.

Signed-off-by: Syam G Krishnan <syamgk@gmail.com>

Signed-off-by: Syam G Krishnan <syamgk01@gmail.com>

Implement part [MSC2228](https://github.com/matrix-org/matrix-doc/pull/2228). The parts that differ are:

* the feature is hidden behind a configuration flag (`enable_ephemeral_messages`)
* self-destruction doesn't happen for state events
* only implement support for the `m.self_destruct_after` field (not the `m.self_destruct` one)
* doesn't send synthetic redactions to clients because for this specific case we consider the clients to be able to destroy an event themselves, instead we just censor it (by pruning its JSON) in the database