Add support for ST 2101 Core Id

[bradh]

What is the use case for your proposed feature? Please describe.
MISB just released ST 2101 for insertion of core identifier (per ST 1204) into the SEI space for H.264/H.265.

Describe the solution you'd like
We should implement that for reading and writing.

Describe alternatives you've considered
N/A

Additional context
Full implementation relies on getting SEI writing working, which need changes at the ffmpeg level.