[DX] Begin adding support for pipeline state

DirectX shader pipeline state validation information is a fairly
complicated to serialize data structure. This patch adds the first bit
of support for reading and writing the runtime info structure which
comes first in the encoded data.

Subsequent patches will flesh out the remaining fields of the data
structure.

There is no official documentation for the format, but the format is
roughly documented in the code comment here:
https://github.com/microsoft/DirectXShaderCompiler/blob/main/include/dxc
/DxilContainer/DxilPipelineStateValidation.h#L731

Reviewed By: python3kgae

Differential Revision: https://reviews.llvm.org/D141649