[HLSL] Add Load overload with status (#166449)
This PR adds a Load method for resources, which takes an additional
parameter by reference, status. It fills the status parameter with a 1
or 0, depending on whether or not the resource access was mapped.
CheckAccessFullyMapped is also added as an intrinsic, and called in the
production of this status bit.
Only addresses DXIL for the below issue:
https://github.com/llvm/llvm-project/issues/138910
Also only addresses the DXIL variant for the below issue:
https://github.com/llvm/llvm-project/issues/99204
