Ability to see which 'friends' are in a chat.

### Your use case

#### What would you like to do?
I would like to be able to see which friends are in a group chat.
#### Why would you like to do it?
I want to know if I know anyone in a certain environment, as that can change things. :)
#### How would you like to achieve it?
An option in the room info menu (where the listing of users is)

### Have you considered any alternatives?

Not really

### Additional context

I understand that matrix doesn't have any "friending" system (although I believe it should!) but it could show just people you happen to be in a 'dm room' with.