Refactor GroupCall participant management

This refactoring brings a number of improvements to GroupCall, which I've unfortunately had to combine into a single commit due to coupling:

- Moves the expiration timestamp field on call membership state to be per-device
- Makes the participants of a group call visible without having to enter the call yourself
- Enables users to join group calls from multiple devices
- Identifies active speakers by their call feed, rather than just their user ID
- Plays nicely with clients that can be in multiple calls in a room at once
- Fixes a memory leak caused by the call retry loop never stopping
- Changes GroupCall to update its state synchronously, and write back to room state asynchronously
  - This was already sort of halfway being done, but now we'd be committing to it
  - Generally improves the robustness of the state machine
  - It means that group call joins will appear instant, in a sense

For many reasons, this is a breaking change.

src/utils.ts

@@ -694,3 +694,16 @@ export function sortEventsByLatestContentTimestamp(left: MatrixEvent, right: Mat
 export function isSupportedReceiptType(receiptType: string): boolean {
     return [ReceiptType.Read, ReceiptType.ReadPrivate].includes(receiptType as ReceiptType);
 }
+
+/**
+ * Determines whether two maps are equal.
+ * @param eq The equivalence relation to compare values by. Defaults to strict equality.
+ */
+export function mapsEqual<K, V>(x: Map<K, V>, y: Map<K, V>, eq = (v1: V, v2: V): boolean => v1 === v2): boolean {
+    if (x.size !== y.size) return false;
+    for (const [k, v1] of x) {
+        const v2 = y.get(k);
+        if (v2 === undefined || !eq(v1, v2)) return false;
+    }
+    return true;
+}