Add setRate, setValue and iOS AirPlay features

[Sun3]

It would be great to add setRate and setValue features, really needed. Also for iOS it would be great to add the routePickerButton to play audio to Apple TV (AirPlay).

Dart:

static const _nativeMethodSetRate = "setRate";
static const _nativeMethodSetRateArgRateInDouble = "rateInDouble";
static const _nativeMethodSetVolume = "setVolume";
static const _nativeMethodSetStateArgVolumeInDouble = "volumeInDouble";

static const _nativeMethodShowRoutePickerView = "showRoutePickerView"; // iOS Only AirPlay

  void setRate(double rate) {
    _invokeNativeMethod(
      _nativeMethodSetRate,
      arguments: <String, dynamic>{_nativeMethodSetRateArgRateInDouble: rate},
    );
  }

  void setVolume(double volume) {
    _invokeNativeMethod(
      _nativeMethodSetVolume,
      arguments: <String, dynamic>{_nativeMethodSetStateArgVolumeInDouble: volume},
    );
  }

void showRoutePickerView() {
  _invokeNativeMethod(_nativeMethodShowRoutePickerView);
}

Kotlin:

private const val NATIVE_METHOD_SET_RATE = "setRate"
private const val NATIVE_METHOD_SET_RATE_ARG_DOUBLE = "rateInDouble"
private const val NATIVE_METHOD_SET_VOLUME = "setVolume"
private const val NATIVE_METHOD_SET_VOLUME_ARG_DOUBLE = "volumeInDouble"

NATIVE_METHOD_SET_RATE -> {
  withArgument(call, NATIVE_METHOD_SET_RATE_ARG_DOUBLE) { rateInDouble: Double ->
    service.setRate(rateInDouble)
  }
}
NATIVE_METHOD_SET_VOLUME -> {
  withArgument(call, NATIVE_METHOD_SET_VOLUME_ARG_DOUBLE) { volumeInDouble: Double ->
    service.setVolume(volumeInDouble)
  }
}

Swit:

case "setRate":
    let arguments = call.arguments as! NSDictionary
    let rateInDouble =  arguments["rateInDouble"] as! Double
    self.setRate(rateInDouble: rateInDouble)

case "setVolume":
    let arguments = call.arguments as! NSDictionary
    let volumeInDouble =  arguments["volumeInDouble"] as! Double
    self.setVolume(volumeInDouble: volumeInDouble)

private func setRate(rateInDouble: Double) {
    // Since setting rate starts playing audio, let's check if player is paused, and keep it paused.
    let isMediaPlayerPlaying = player.rate
    player.rate = Float(rateInDouble)
    playerRate = Float(rateInDouble)
    if (isMediaPlayerPlaying == 0) {
        player.pause()
    }
}

private func setVolume(volumeInDouble: Double) {
    player.volume = Float(volumeInDouble)
}

private func showRoutePickerView() {
    if (routePickerView != nil) {
        if let routePickerButton = routePickerView.subviews.first(where: { $0 is UIButton }) as? UIButton {
            routePickerButton.sendActions(for: .touchUpInside)
        }
    }
}

Thank you.