[HLSL] Add execution testing of Root Signatures

[inbelic]

This is an umbrella issue that tracks creating sufficient test coverage of executing shaders with root signatures.

It is complete when there is complete test coverage of using root signatures in compute and graphics shaders, which will be resolved when all sub-issues are resolved.

[inbelic]

Marking as unblocked as llvm/offload-test-suite#208 has landed to allow testing StaticSamplers and the obj2yaml portions of #118897 are completed.

[inbelic]

Closing as completed as all sub-issues are finished.