Update SDK to be consumed by Element Call's CallViewModel

Update the public API to export the primitives and operators the call
model needs, and change `LocalMediaInputs` from observable flags to
immediate booleans with imperative setters. Add session timings, media
quality and capture settings as configuration options, and allow the
host to override the transport discovery with explicit URLs.

sdk/README.md

@@ -9,8 +9,9 @@ in [`SdkMigration.md`](./SdkMigration.md).
 
 **Status:** first implementation. `createMatrixRTCClient` joins the session, connects to
 the transport, publishes the local media and exposes every member's media; the
-development harness and its e2e tests in `playwright/sdk` drive it. It depends on
-nothing in Element Call's `src/`; Element Call does not consume it yet.
+development harness and its e2e tests in `playwright/sdk` drive it, and Element
+Call's own `CallViewModel` is built on it. It depends on nothing in Element Call's
+`src/`.
 
 ## Using it
 
@@ -29,10 +30,11 @@ const rtcClient = createMatrixRTCClient(
   client, // a matrix-js-sdk MatrixClient, logged in and syncing
   room, // the matrix-js-sdk Room, from client.getRoom() once the join has synced
   {
-    microphoneEnabled$: constant(true),
-    cameraEnabled$: constant(true),
+    microphoneEnabled: true,
+    cameraEnabled: true,
     audioInputDeviceId$: constant(undefined),
     videoInputDeviceId$: constant(undefined),
+    audioOutputDeviceId$: constant(undefined),
     videoProcessor$: constant(undefined),
   },
   {