[SDK] Move SFU authentication into livekit/auth and choose the endpoint by role

The OpenID flow moves to src/livekit/auth/openID.ts with the SFU config
types in a sibling file, takes an options object, and replaces the
MatrixRTC mode with the role we take on the transport plus the session's
slot ID instead of a hard-coded m.call#ROOM.

This changes behaviour: publishers on a livekit_service_url transport
always use the legacy /sfu/get endpoint, so that subscribers can predict
their user:device participant identity, and subscribers always use the
default /get_token endpoint. The MatrixRTC mode no longer influences which
endpoint is used.

On the SDK this lands as sdk/src/media-backend/livekit/auth/ with the connection map, the discriminated connection state and the client-server API flow of the following commits of element-hq/element-call#4331, which rewrite the same files:
- Model ConnectionState as a discriminated union
- Show the whole transport in debug UI and logs (SDK part)
- Let the publishing Connection authenticate itself
- Reduce ConnectionManager to a ConnectionMap
- Use the unstable LiveKit transport type
- Identify transports by server name as well as URLs
- Get SFU tokens and delegate delayed leaves through the MSC4195 CS API
- Fall back to get_token as subscriber on widget API errors
- Share a connection between homeservers using the same JWT service
- Make the auth choice mode independent again

Co-authored-by: Johannes Marbach <n0-0ne+github@mailbox.org>
(cherry picked from commit adb380cd9ed108856e42d992fc03ced8c44f1e56)

sdk/src/media-backend/livekit/DataChannel.ts

@@ -6,6 +6,7 @@ Please see LICENSE in the repository root for full details.
 */
 
 import {
+  ConnectionState as LivekitConnectionState,
   type RemoteParticipant,
   type Room as LivekitRoom,
   RoomEvent,
@@ -22,14 +23,17 @@ import {
 } from "rxjs";
 
 import { type Behavior } from "../../reactive/Behavior";
-import { type ObservableScope } from "../../reactive/ObservableScope";
+import {
+  type Epoch,
+  type ObservableScope,
+} from "../../reactive/ObservableScope";
 import { type DataPacket } from "../api";
-import { type Connection, ConnectionState } from "./Connection";
-import { type IConnectionManager } from "./ConnectionManager";
+import { type Connection } from "./Connection";
+import { type ConnectionMap } from "./ConnectionMap";
 
 interface Props {
   scope: ObservableScope;
-  connectionManager: IConnectionManager;
+  connectionMap$: Behavior<Epoch<ConnectionMap>>;
   /** The local member's connection, which carries what we send. */
   connection$: Behavior<Connection | null>;
 }
@@ -47,13 +51,13 @@ export interface DataChannel {
  */
 export function createDataChannel$({
   scope,
-  connectionManager,
+  connectionMap$,
   connection$,
 }: Props): DataChannel {
   const decoder = new TextDecoder();
   const encoder = new TextEncoder();
 
-  const rooms$ = connectionManager.connectionManagerData$.pipe(
+  const rooms$ = connectionMap$.pipe(
     map(({ value }) => value.getConnections().map((c) => c.livekitRoom)),
     distinctUntilChanged(
       (a, b) => a.length === b.length && a.every((room, i) => room === b[i]),
@@ -79,7 +83,12 @@ export function createDataChannel$({
 
   const sendData = async (topic: string, text: string): Promise<void> => {
     const connection = connection$.value;
-    if (connection?.state$.value !== ConnectionState.LivekitConnected)
+    const state = connection?.state$.value;
+    if (
+      connection === null ||
+      state?.state !== "authenticated" ||
+      state.livekitState !== LivekitConnectionState.Connected
+    )
       throw new Error("Cannot send data: the local transport is not connected");
     await connection.livekitRoom.localParticipant.publishData(
       encoder.encode(text),