We now prevent these variations:
* <hr/>
* <hr />
* <br/>
* <br />
We could enforce similar consistency for other void
tags, if we wished, but these two are particularly
prevalent.
Edited the warning to clearly state that most members/most stream members
will be notified on using wildcard mentions, along with the specific
mention (e.g. @ALL, @everyone and @stream).
Did a separate check for all wildcard mentions in util.js and stored the
corresponding mention in wildcard_mention inside compose.js.
Fixes: #13636