Explicit specification of inter-layer reference pictures, using a layer-specific GOP structure, with 0.x syntax (0=same POC, x=reference layer).
When ExplicitILRP is true, AllowablePredDirection should not be used or left to default values (all zero), and inter-layer reference pictures are no longer inserted automatically.

There are cases where numberOfAdditionalCabacZeroBytes = 0,
so a vector of size 0 is created and we can't access the first
element of this vector.

Use vector of arrays instead of vector

Includes:
- fix syntax element names for tracing
- add validation checks
- move validation check to correct place
- define `enum HrdType` for indexing by `NAL` or `VCL`
- consistently use `bp` variable name for BP SEI objects
- use `static_vector` instead of having separate variable for array size