[pending] Add METADATA_TYPE_USER_DATA_UNREGISTERED

[joelsole]

This provides the text for the user data unregistered metadata as proposed in CWG-G007. Pending CWG approval; this text serves as a reference against the WD.

[peterderivaz]

You currently pass in metadata_obu( obu_size ). Did you instead want to pass in metadata_obu( obu_size - 1) to leave space for trailing bits (as in the AV2 version)?

And did you want to subtract the number of bytes used to encode the metadata_type as well?

[joelsole]

Did you instead want to pass in metadata_obu( obu_size - 1) to leave space for trailing bits (as in the AV2 version)?

Adjusting the value in the next commit.

And did you want to subtract the number of bytes used to encode the metadata_type as well?

That's right. I'll use the variable Leb128Bytes from function leb128(), as in the AV2 case.