Add `event_stream_ordering` column to membership state tables (#14979)

This adds an `event_stream_ordering` column to `current_state_events`,
`local_current_membership` and `room_memberships`. Each of these tables
is regularly joined with the `events` table to get the stream ordering
and denormalising this into each table will yield significant query
performance improvements once used. Includes a background job to
populate these values from the `events` table.

Same idea as https://github.com/matrix-org/synapse/pull/13703.

Signed off by Nick @ Beeper (@fizzadar).