audio: add file streaming support

When sharing a file, its audio will also be decoded and sent. Audio and
video are synchronized for the first loop of the file only. Further
loops desynchronize them as the audio and video are decoded separately
instead of with the same decoder.

Device audio is muted while streaming. Mixing of the microphone with the
file audio will be added in a later patch.

Adds common audio decoders for file streaming.

Change-Id: Id0593ce4f2d32c249eb7a9672b0091c0d6e07a00