message: adding createMediaStreamSource
  should create BaseContext class to better handle this case
diff: @@ -198,6 +198,11 @@ export class Context extends Emitter<"statechange" | "tick"> implements BaseAudi
  createWaveShaper(): WaveShaperNode {
  return this._context.createWaveShaper();
  }
  + createMediaStreamSource(stream: MediaStream): MediaStreamAudioSourceNode {
  + this.assert(isAudioContext(this._context), "Only available on online audio context");
  + // @ts-ignore
  + return this._context.createMediaStreamSource(stream);
  + }
  decodeAudioData(audioData: ArrayBuffer): Promise<AudioBuffer> {
  return this._context.decodeAudioData(audioData);
  }
  