Bug 1019291 - Construct Annex B samples in the decoder. r=cpeace

Move Annex B sample formatting from the demuxer to a
static utility function. Return NAL unit syntax
samples by default, since more platforms prefer to
unpack the AVCC data themselves.

Pass the raw AVCC payload to ffmpeg through its extradata
field. It can handle either sample format, expecting one or
the other depending on whether extradata is present.

Pass input samples through a new WMFOutputSource::Input
method. Save a reference to the VideoDecoderConfig in the
WFMVideoOutputSource and use it to convert samples to
Annex B before forwarding them to the MFTDecoder.