Make tiles be based on RTC member

[toger5]

Currently a tile is shown whenever livekit has a participant.
This is wrong in a couple of situations:

• If there are members in the livekit room that are not in the matrix room. (This can happen since we do not have any control over what the lk server is doing)
• If a user is joined in matrix but they struggle to create a livekit connection that is a state we want to show to the user but currently we dont know about that. Since without a livekit participant we dont have any tile.
• If someone leaves but still continue connects to livekit, we can remove their tile.
• In an encrypted room, users without a matrix rtc membership cannot get the call keys, so their streams will be irrelevant anyways + they cannot do anything with the stream from others. -> there is no reason to add them as tiles.

[CLAassistant]

All committers have signed the CLA.

[hughns]

One "rough edge" on this is that when a remote participant leaves the call, they are shown as "Waiting for media..." whilst the animation to remove the tile from the screen is playing.

This is fixed indirectly using the animated loading border,

The "animated loading border" is now in #2858 for consideration.

[hughns]

This is ready for the next round of review.

[hughns]

With regards to the visual design/representation: I think we should get it merged as-is (with the "Waiting for media...") and then tackle the representation before we do a release.

[toger5]

Oh I cannot approve my own PR ;) So @hughns you need to approve on my behave