This removes mentions from ChatBarCache and instead sets mentions as an anchor using the QTextCursor. Saving and restoring the chatbar text content is then done using QTextDocumentFragments which retain the rich text formatting.
There's two parts to making this work mainly:
1. Use getEvent instead of findInTimeline so the related event is
actually found.
2. Close the dialog once a reply relation is found, so you can easily
reply in the chat bar.
There's a bug in how we're using this function in room search, but we
definitely don't want it to crash. The event is technically not in the
timeline, so we were dereferencing an invalid iterator or whatever.
This happens semi-frequently to me and others - we reply to a user who
has left the room. Sometimes this is useful (for example, bringing up a
previous topic) but in most cases this is accidental, and almost
guaranteed to happen if you turned off join/leave events.
So I added a reminder when replying - which manifests as a small label
in the chatbar - that the user has left and can't be notified of your
reply.
