[DX] [ObjectYAML] Support DX shader feature flags

DXContainers contain a feature flag part, which stores a bitfield used
to denote what underlying hardware features the shader requires. This
change adds feature flags to the DXContainer YAML tooling to enable
testing generating feature flags during HLSL code generation.

Depends on D133980

Reviewed By: lhames

Differential Revision: https://reviews.llvm.org/D134315