[clang] [HLSL] Make sure `isSigned` flag is set on target type for `TypedBuffer` resources with signed int vectors (PR #130223)

[Helena Kotas via cfe-commits]

hekota wrote:

> LGTM for DXIL. Is there a plan to do this with SPIR-V too?

SPIR-V is generating different target type and it does not seem to have the 'signed' flag:
See https://github.com/llvm/llvm-project/blob/fbf0276b6a7a7a4508c373cf87fc349569652659/clang/lib/CodeGen/Targets/SPIR.cpp#L396


https://github.com/llvm/llvm-project/pull/130223