There is no need to duplicate check chat messages when they are being
edited but not having their message text changed. This was leading to
a validation error when adding/removing an upload but not changing the
message text.
Only allow maximum of 6000 characters for chat messages when they
are created or edited. A hidden setting can control this limit,
6000 is the default.
There is also a migration here to truncate any existing messages to
6000 characters if the message is already over that and if the
chat_messages table exists. We also set cooked_version to NULL
for those messages so we can identify them for rebake.
Follow up to 766bcbc684
This fixes a gaffe from that commit where I passed in the
guardian to ChatMessageUpdater but then forgot to remove
the old way of setting the guardian and user instance variables
from the chat_message that was passed in.
Also, it moves the ensure_can_edit_message! check from the
controller into ChatMessageUpdater so all the access
checks are in the same place.
This commit adds last_editor_id to ChatMessage for parity with Post in
core, as well as adding user_id to the ChatMessageRevision record since
we need to know who is making edits and revisions to messages, in case
in future we want to allow more than just the current user to edit chat
messages. The backfill for data here simply uses the record's creating
user ID, but in future if we allow other people to edit the messages it
will use their ID.
