Transform automatically non allowed character in Nickname ( Matrix -> XMPP )

[JokerGermany]

Describe the bug
When a Nickname of Matrix user contains in XMPP not allowed character like emoji, they should be converted automatically to prevent that other xmpp users can't read his messages.

To Reproduce

1. Change your Global Nick of a matrix account to something with a emoji in it
2. join a XMPP Room
3. Send a message
4. Some XMPP User won't be able to read the messages.

Expected behavior
Variant 1:
The bridge changed the nickname of the Person automatically.

Variant 2:
The bridge messages the user and tell him, that he need to change his nickname otherwise not every XMPP User will be able to read his messages.

Additional context
For Variant 2:
@maranda implemented that the bridge forward changing the roomnick:
maranda@6a0743b
maranda@86b5fbf
maranda@dfdc29f
maranda@49a15c5
If this is not implemented, the Global Name has to be changed!

[Half-Shot]

I suspect we want to do variant 1. I actually thought we did this already! Calling this out as a T-major since it's hard to easily workaround.