Changes in this update:
- Added the SpeechSynthesizer, an implementation of the SpeechRecognizer capability agent.
- Implemented a reference MediaPlayer based on [GStreamer](https://gstreamer.freedesktop.org/) for audio playback.
- Added the MediaPlayerInterface that allows you to implement your own media player.
- Updated ACL to support asynchronous receipt of audio attachments from AVS.
Bug Fixes:
-Some intermittent unit test failures were fixed.
Known Issues:
-ACL's asynchronous receipt of audio attachments may manage resources poorly in scenarios where attachments are
received but not consumed.
- When an AttachmentReader does not deliver data for prolonged periods MediaPlayer may not resume playing the
delayed audio.
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