Implement the new unified grid layout

Here I've implemented an MVP for the new unified grid layout, which scales smoothly up to arbitrarily many participants. It doesn't yet have a special 1:1 layout, so in spotlight mode and 1:1s, we will still fall back to the legacy grid systems.

Things that happened along the way:
- The part of VideoTile that is common to both spotlight and grid tiles, I refactored into MediaView
- VideoTile renamed to GridTile
- Added SpotlightTile for the new, glassy spotlight designs
- NewVideoGrid renamed to Grid, and refactored to be even more generic
- I extracted the media name logic into a custom React hook
- Deleted the BigGrid experiment

src/state/CallViewModel.ts

@@ -154,11 +154,11 @@ class UserMedia {
     this.vm = new UserMediaViewModel(id, member, participant, callEncrypted);
 
     this.speaker = this.vm.speaking.pipeState(
-      // Require 1 s of continuous speaking to become a speaker, and 10 s of
+      // Require 1 s of continuous speaking to become a speaker, and 60 s of
       // continuous silence to stop being considered a speaker
       audit((s) =>
         merge(
-          timer(s ? 1000 : 10000),
+          timer(s ? 1000 : 60000),
           // If the speaking flag resets to its original value during this time,
           // end the silencing window to stick with that original value
           this.vm.speaking.pipe(filter((s1) => s1 !== s)),