[clang] [HLSL] reenable add packoffset in AST (PR #91474)

[Xiang Li via cfe-commits]

python3kgae wrote:

> When reapplying a change that was reverted, please include enough information in the description so that it can be understood without having to dig up the old change. Something like:
> 
> > [HLSL] reenable add packoffset in AST
> > This reapplies [c5509fe](https://github.com/llvm/llvm-project/commit/c5509fedc5757fffece385d9d068e36b26793ade) "[HLSL] Support packoffset attribute in AST (#89836)" with a fix for the test failure caused by missing -fnative-half-type.
> > Since we have to parse the attribute manually in ParseHLSLAnnotations, we could create the ParsedAttribute with a integer offset parameter instead of string. This approach avoids parsing the string if the offset is saved as a string in HLSLPackOffsetAttr.

Update. Thanks a lot.

https://github.com/llvm/llvm-project/pull/91474