[HLSL] Buffer SRV type

[bogner]

We somehow haven't gotten around to adding the the Buffer<T> type to HLSL. This is similar to RWBuffer (but it's an SRV) and StructuredBuffer (but it's a TypedBuffer). The logic to do this should more or less match the definition of RWBuffer, except read-only.

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Justin Bogner (bogner)

We somehow haven't gotten around to adding the the `Buffer<T>` type to HLSL. This is similar to `RWBuffer` (but it's an SRV) and `StructuredBuffer` (but it's a TypedBuffer). The logic to do this should more or less match the definition of `RWBuffer`, except read-only.