Room/MUC should have the same Room rights as the bridged Room

Describe the bug
When i have a Matrix room where only Moderators/Admins can write, XMPP-Usern shouldn't be able to write as well.

To Reproduce

1. Create a Matrix Room where only Moderators/Admins can write
2. join it with a XMPP Account.
3. you can write messages which won't be bridged to the Matrix-Room but can be seen by other XMPP-Users.

Expected behavior
The XMPP/Matrix rights should be nearly* the same
(* as far as possible. e.G. when a XMPP User joins a Matrix Room where only Moderators and Admins are allowed to join, then a moderated MUC should be created.)

Additional context
Perhaps a quick and dirty solution for Moderated Rooms/MUC could be allowing to write, but if the other bridged MUC/Room "reject" the message, it get deleted in the Gateway-Room/MUC aswell.

Reproduce the issue using the Matrix room and XMPP account steps, then trace the bridge's handling of room permissions and MUC message delivery. Done means XMPP users cannot post where the bridged Matrix room rejects them, with the reported moderated-room behavior handled consistently.