message: Use mxid as sender name on set display name
  As it was, "<New name> set their display name to <New name>" which
  is unhelpful because you never knew them as "<New name>" before.
  They would previously have been displayed with their matrix ID, so
  that's what should be here.
diff: @@ -58,7 +58,7 @@ function textForMemberEvent(ev) {
  });
  } else if (!prevContent.displayname && content.displayname) {
  return _t('%(senderName)s set their display name to %(displayName)s.', {
  - senderName,
  + senderName: ev.getSender(),
  displayName: content.displayname,
  });
  } else if (prevContent.displayname && !content.displayname) {
  