Start refactoring some business logic into view models

As Element Call grows in complexity, it has become a pain point that our business logic remains so tightly coupled to the UI code. In particular, this has made testing difficult, and the complex semantics of React hooks are not a great match for arbitrary business logic. Here, I show the beginnings of what it would look like for us to adopt the MVVM pattern. I've created a CallViewModel and TileViewModel that expose their state to the UI as rxjs Observables, as well as a couple of helper functions for consuming view models in React code.

This should contain no user-visible changes, but we need to watch out for regressions particularly around focus switching and promotion of speakers, because this was the logic I chose to refactor first.

package.json

@@ -18,6 +18,7 @@
   },
   "dependencies": {
     "@juggle/resize-observer": "^3.3.1",
+    "@livekit/components-core": "^0.7.0",
     "@livekit/components-react": "^1.1.0",
     "@matrix-org/olm": "https://gitlab.matrix.org/api/v4/projects/27/packages/npm/@matrix-org/olm/-/@matrix-org/olm-3.2.14.tgz",
     "@opentelemetry/api": "^1.4.0",
@@ -37,6 +38,7 @@
     "@react-aria/tabs": "^3.1.0",
     "@react-aria/tooltip": "^3.1.3",
     "@react-aria/utils": "^3.10.0",
+    "@react-rxjs/core": "^0.10.7",
     "@react-spring/web": "^9.4.4",
     "@react-stately/collections": "^3.3.4",
     "@react-stately/select": "^3.1.3",
@@ -70,6 +72,7 @@
     "react-router-dom": "^5.2.0",
     "react-use-clipboard": "^1.0.7",
     "react-use-measure": "^2.1.1",
+    "rxjs": "^7.8.1",
     "sdp-transform": "^2.14.1",
     "tinyqueue": "^2.0.3",
     "unique-names-generator": "^4.6.0",