Android - playback, position, seek methods executed in background thread

[brunolau]

Platforms affected

Android

Motivation and Context

By executing the playback, position, seek, duration and other media manipulation methods by a background thread, performance gain is achieved mostly when multiple audio files are prepared at the same time.

Description

play, pause, stop, seek, setRate, duration methods as well as onPrepared event are executed and handled by a background thread.

Testing

By running in my local application

Checklist

• [ ] I've run the tests to see all new and existing tests pass
• [ ] I added automated test coverage as appropriate for this change
• [ ] Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• [ ] If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• [x] I've updated the documentation if necessary