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/livekit/auth/types.ts

@@ -5,6 +5,17 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
+import { type UnstableLivekitTransport } from "matrix-js-sdk/lib/matrixrtc";
+
+/**
+ * Data identifying a transport and the homeserver to which it belongs, so
+ * consumers know how to reach it.
+ */
+export interface TransportLocator {
+  transport: UnstableLivekitTransport;
+  serverName: string;
+}
+
 /**
  * Configuration and access tokens provided by the SFU on successful authentication.
  */