[HLSL][DirectX] Texture and Sampler resource types and operations

[damyanp]

• Implement llvm intrinsics for texture sampling and lower them to the dxil ops
• Implement load/store (and other non-sampling) intrinsics for textures and lower them to dxil ops
• Implement builtins for texture sampling operations on HLSLResource types that will lower to the llvm intrinsics

[damyanp]

We should consider when implementing this microsoft/DirectXShaderCompiler#5744