New ringing UI

This implements the new ringing UI by showing a placeholder tile for the participant being dialed, rather than an overlay.

src/state/CallViewModel/CallNotificationLifecycle.ts

@@ -89,7 +89,6 @@ export interface Props {
  * `callPickupState$` The current call pickup state of the call.
  *  - "unknown": The client has not yet sent the notification event. We don't know if it will because it first needs to send its own membership.
  *     Then we can conclude if we were the first one to join or not.
- *     This may also be set if we are disconnected.
  *  - "ringing": The call is ringing on other devices in this room (This client should give audiovisual feedback that this is happening).
  *  - "timeout": No-one picked up in the defined time this call should be ringing on others devices.
  *     The call failed. If desired this can be used as a trigger to exit the call.
@@ -131,15 +130,9 @@ export function createCallNotificationLifecycle$({
   ) as Behavior<Epoch<boolean>>;
 
   /**
-   * Whenever the RTC session tells us that it intends to ring the remote
-   * participant's devices, this emits an Observable tracking the current state of
-   * that ringing process.
+   * The state of the current ringing attempt, if the RTC session is indeed
+   * ringing the remote participant's devices. Otherwise `null`.
    */
-  // This is a behavior since we need to store the latest state for when we subscribe to this after `didSendCallNotification$`
-  // has already emitted but we still need the latest observable with a timeout timer that only gets created on after receiving `notificationEvent`.
-  // A behavior will emit the latest observable with the running timer to new subscribers.
-  // see also: callPickupState$ and in particular the line: `return this.ring$.pipe(mergeAll());` here we otherwise might get an EMPTY observable if
-  // `ring$` would not be a behavior.
   const remoteRingState$: Behavior<"ringing" | "timeout" | "decline" | null> =
     scope.behavior(
       sentCallNotification$.pipe(