[HLSL] Add appropriate support for loop metadata kinds

[bob80905]

Like #137386, the DXC validator accepts certain metadata nodes of the loop kind.
The whitelist needs to be expanded to allow for certain metadata nodes. Specifically, llvm.loop.unroll.full, llvm.loop.unroll.disable, and
llvm.loop.unroll.count should be allowed, but not "llvm.loop.mustprogress"
Additionally, the new loop metadata node kinds should be validated in the same way that the dxc validator validates. The presence of these metadata kinds is not enough. For example, the unroll count metadata kind should have recursive validation, and that if the number of operands is not 1 nor 2, a validation error should be emitted. Reference needs to be made to the validator to accurately mimic validation behavior.