[DirectX] Add dx.CBuffer handling to DXILResourceAccess pass

[hekota]

Codegen for constant buffers generates llvm.dx.resource.getpointer and getelementptr intrinsics to access the constant values. DXILResourceAccess pass needs to translate these to llvm.dx.resource.load.cbuffer intrinsic calls.

[damyanp]

No longer required now we're doing #124630