[HLSL][SPIRV] Implement Load(int, out uint) overloads for buffer types for SPIR-V

[s-perron]

All of the HLSL buffer (and texture) types have overloads of Load like RWBuffer::Load(int, uint). We need to implement these.

These functions should call the appropriate buffer load intrinsic directly.

In SPIR-V, DXC will map loads to OpImageSparseRead rather than OpImageRead

[bob80905]

I'm changing this issue, it's no longer going to be about implementing a SPIR-V intrinsic, since that is no longer going to be the route we go down. Instead, this issue should just be about implementing the SPIR-V side of the status overload of load.