Redacting membership events should immediately reset the displayname & avatar of room members

[matrixbot]

Created by @ matthew:matrix.org.

This is useful for killing offensive avatars & nicks immediately; currently it gets cached until the next initial sync

[giomfo]

The client must update the local room state on redaction event which concerned membership events.

[giomfo]

Blocked by SYN-724 (prev_content is totally pruned by the server on redacted membership event).

[ylecollen]

What i've done on the android client
https://github.com/matrix-org/matrix-android-sdk/blob/develop/matrix-sdk/src/main/java/org/matrix/androidsdk/data/EventTimeline.java#L625

https://github.com/matrix-org/matrix-android-sdk/blob/develop/matrix-sdk/src/main/java/org/matrix/androidsdk/data/EventTimeline.java#L1306

When a membership event is redacted, the client always requests the up-to date-roomState to the server and forces the room history reload (it is already done on the IOS client) but it also refresh the members list and the room settings.
Indeed, the redaction must not update the live state because it might not concern it.

eg with this room history

... older messages
message_1 : A renames this room to Name1
... some other messages
message_2 : A renames this room to Name2
... other messages

If message_1 is redacted, the room name must not be cleared because it has been updated by message_2.