Add ability to expand and interact with room topic in join room screen

[marwing]

Is your feature request related to a problem? Please describe.
In the join room screen, the room topic is limited to 3 lines, without the ability to show the remaining content or open embedded links.

Describe the solution you'd like
Provide a way to expand the topic, similar to the room details screen. The expansion should also make links clickable.

Describe alternatives you've considered

Alternative	Problem
Joining the room first and checking the topic after	I can't check the room info before joining
Use another client	This is undesirable because this is a lot of overhead and I would need to somehow get the room alias/id into the other client
Just don't care about the topic	Sometimes I do
Make a screenshot and let iOS extract links	This works reasonably well for links that are fully visible, but is obviously not viable long-term and only addresses part of the problem

Additional context
Example screen with cut of topic