Show the number of participants in the room list for element call room.

### Your use case

#### What would you like to do?
The legacy room list used to have this feature, it will show the number of current participants when using element call, similar to the behavior of Discord. Now this feature has been removed.

#### Why would you like to do it?
Now this indicator has been move to the chat room, which is less obvious.

#### How would you like to achieve it?
Recover this feature like the one in the legacy room list.

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

Start by locating the current room-list entry point and the Element Call participant data, then compare it with the legacy room-list behavior described in the issue. Done means the room list visibly shows the current participant count for Element Call rooms, while the existing chat-room indicator remains available.

Written by the indexing model from the issue text.