Cast: Implement connectionless (Cast.API_CXLESS) device controller

[peterhel]

Cast: Implement connectionless (Cast.API_CXLESS) device controller

Summary

Modern Cast SDK clients — and real apps such as Amazon Prime Video, YouTube,
Netflix — drive the Cast device over the connectionless Cast API
(Cast.API_CXLESS) rather than the classic connection-based path that microG
implemented. As a result, casting from these apps never worked on microG: the
session would start and then stall indefinitely.

This PR implements the connectionless device-controller surface. With it, the
real Amazon Prime Video app launches its own receiver and plays a DRM title
end to end on a Chromecast, cast from a de-Googled phone.

Builds on #3567 (which makes the framework start a session when a Cast route is
selected); that session is the trigger that binds the device controller this PR
completes.

The problem

The connectionless client binds the same ICastDeviceController service, but
its handshake differs from the classic client:

• The classic client passes its listener in the GetServiceRequest "listener"
  extra and connects lazily on the first launch/sendMessage.
• The connectionless client instead delivers its listener out-of-band via
  setListener(), then calls connect(), and waits for the service to call
  ICastDeviceControllerListener.onConnectedWithResult before it will launch an
  application. It is otherwise purely reactive.

microG implemented only the classic path. So a connectionless client bound the
service, called setListener/connect (transactions microG didn't handle, and
which were silently dropped because they are oneway), never received
onConnectedWithResult, and stayed "not connected" forever. Withholding the
cxless_* features to force the classic path instead just made the SDK decide
microG was too old and fail with ConnectionResult=2.

The fix

The transaction numbers in microG's AIDL already matched the framework — the
connectionless methods were simply absent. The change is additive:

• ICastDeviceController.aidl — add connect() (txn 17),
  setListener(ICastDeviceControllerListener) (18), unregisterListener() (19).
• ICastDeviceControllerListener.aidl — add onConnectedWithResult(int)
  (txn 14), the readiness signal.
• CastDeviceControllerImpl.java:
  • connect() opens the CastV2 channel and emits
    onConnectedWithResult(SUCCESS).
  • setListener() stores the out-of-band listener.
  • onSendMessageSuccess is now reported from the outgoing sendMessage,
    keyed by that send's requestId. Previously it was reported from inbound
    messages using the response's id, which completed a non-existent client task
    and threw a RemoteException. Inbound messages now go solely through
    onTextMessageReceived.
  • The client's listener binder is watched with linkToDeath; if the client
    process dies without a clean disconnect(), the device connection (and its
    reader thread) is torn down instead of leaked.
• CastDeviceControllerService.java — advertise the requested API features
  via ConnectionInfo so the client's availability check passes.

Connectionless handshake (for reference)

bind CAST service (cxless features, EXTRA_CAST_DEVICE, connectionless_client_record_id)
  → setListener(listener)              [txn 18]
  → connect()                          [txn 17]
  ← onConnectedWithResult(0)           [listener txn 14]   // session becomes "connected"
  → launchApplication(appId, opts)     [txn 13]
  ← onApplicationConnectionSuccess     [listener txn 2]
  → sendMessage(LOAD, media namespace) [txn 9]             // + per-app namespaces
  ← onSendMessageSuccess / onTextMessageReceived

Testing

Validated on a Pixel 2 (LineageOS-for-microG, Android 15) against a Chromecast:

• The real, logged-in Amazon Prime Video app selects the device, microG
  launches Prime's own receiver (appId 17608BC8), Prime completes its
  proprietary registration/settings handshake on
  urn:x-cast:com.amazon.primevideo.cast, LOADs a DRM title, and the title
  plays on the TV — with zero failed listener callbacks.
• A minimal first-party Cast sender plays a clip end to end
  (playerState=PLAYING, currentTime advancing).
• Force-killing the sender mid-session triggers the linkToDeath cleanup
  (device disconnected, no leaked connection).

Notes / scope

• CastMediaRouteController.onSelect remains a stub; it is a separate legacy
  route-control path and does not gate the connectionless flow (the framework's
  session manager binds the device controller directly).
• The auxiliary CAST_API service (id 161 — settings/relay/logging) is still
  unimplemented; it is not on the media path and its absence did not affect
  casting in testing.