Display users in video/voice channels as a list

### Describe the problem As a user in a server looking for someone to talk to in voice chat, I want to be able to see where if a particular group/person is in a voice room, or which room they are in. This could be across multiple spaces. Currently this requires checking each voice room with active participants one at a time. ### Describe the solution you'd like Have the users in a given voice channel displayed in a collapsible list, joined to the room in the space navigation screen. This is similar to other voice first chat apps, such as TeamSpeak, Discord, and Mumble. Due to the issue of many call participants taking up space in the UI, the list could be collapsed over a certain number (retaining the current "live" count badge), or have e.g "+10 more" placeholder. If the default list state (open, closed) is user configurable, then users can opt in to a more voice-first experience. ### Alternatives considered Listing the current voice channel of a user in by their name in the member sidebar. ### Additional context Moved from #2739 into a feature request issue.