Redact message events according to spec and ruma types. Remove content
using events redact() method and insert the redacting event into the
event being redacted.
The new algorithm is simpler. Instead of tracking a list of
disambiguated display names in `Room`, we instead track the display name
ambiguity status in `RoomMember`. This allows a client to generate the
correct name for a member using solely the information available in
`RoomMember`.
The disambiguation algorithm itself now only calculates the set of members
whose ambiguity status had changed instead of producing disambiguated
display names for everyone affected. This is called on each room entry
(join or invite), room entry and profile change, and the updates are
propagated to the affected `RoomMember`s.
The MessageQueue holds MessageEventStub<AnyMessageEventContent> so when
a redaction event is encountered the redacted event's content can be
replaced. The Unsigned field redacted_because is also populated with the
redaction event itself with the addition of a room_id Stub -> full
event.
