[HLSL] Pointers are unsupported in HLSL

HLSL does not support pointers or references. This change generates
errors in sema for generating pointer, and reference types as well as
common operators (address-of, dereference, arrow), which are used with
pointers and are unsupported in HLSL.

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D123167