FLAC: Support channel mask in Vorbis Comments

Source: https://www.ietf.org/archive/id/draft-ietf-cellar-flac-14.html#name-channel-mask

Apparently there's a standardized Vorbis Comments field for the channel mask in FLAC spec now?

Is anyone using it? Probably not. Will it hurt to update the FlacProperties if we encounter it? Also probably not. Also in the case that this is being used, we don't want to overwrite it when writing/stripping tags.

The field is WAVEFORMATEXTENSIBLE_CHANNEL_MASK, which contains the hex-encoded channel mask.

From the spec:

Following are three examples:

• If a file has a single channel, being a LFE channel, the Vorbis comment field is WAVEFORMATEXTENSIBLE_CHANNEL_MASK=0x8.
• If a file has four channels, being front left, front right, top front left, and top front right, the Vorbis comment field is WAVEFORMATEXTENSIBLE_CHANNEL_MASK=0x5003.
• If an input has four channels, being back center, top front center, front center, and top rear center in that order, they have to be reordered to front center, back center, top front center and top rear center. The Vorbis comment field added is WAVEFORMATEXTENSIBLE_CHANNEL_MASK=0x12104.

Start with FlacProperties and the FLAC Vorbis Comments handling, using the linked FLAC specification to confirm the WAVEFORMATEXTENSIBLE_CHANNEL_MASK format. Done means the channel mask is recognized in FLAC properties and is preserved when writing or stripping tags; verify the behavior with the existing FLAC tests.