Identify transports by server name as well as URLs

A transport with only a LiveKit SFU `url` has to be authenticated through
our own homeserver, which needs to know the name of the server owning the
SFU. Carry that name alongside the transport as a TransportLocator,
derived from the member's user ID for remote transports and from the
client's domain for our own, and key the connection map on the SFU URL,
the service URL and the server name together so that `url`, service URL
and combined transport shapes are deduplicated consistently.

src/utils/test-viewmodel.ts

@@ -69,7 +69,7 @@ export function getBasicRTCSession(
       getUserId: () => localRtcMember.userId,
       getDeviceId: () => localRtcMember.deviceId,
       getSyncState: () => SyncState.Syncing,
-      getDomain: () => null,
+      getDomain: () => "example.com",
       getAccessToken: () => "fake-token",
       sendEvent: vitest.fn().mockResolvedValue({ event_id: "$fake:event" }),
       redactEvent: vitest.fn().mockResolvedValue({ event_id: "$fake:event" }),