[HLSL] add loop unroll (#93879)

spec: https://github.com/microsoft/hlsl-specs/pull/263

- `Attr.td` - Define the HLSL loop attribute hints (unroll and loop)
- `AttrDocs.td` - Add documentation for unroll and loop
- `CGLoopInfo.cpp` - Add codegen for HLSL unroll that maps to clang
unroll expectations
- `ParseStmt.cpp` - For statements if HLSL define DeclSpecAttrs via
MaybeParseMicrosoftAttributes
- `SemaStmtAttr.cpp` - Add the HLSL loop unroll handeling

resolves #70114

dxc examples: 
- for loop: https://hlsl.godbolt.org/z/8EK6Pa139
- while loop:  https://hlsl.godbolt.org/z/ebr5MvEcK
- do while: https://hlsl.godbolt.org/z/be8cedoTs 

Documentation:

![Screenshot_20240531_143000](https://github.com/llvm/llvm-project/assets/1802579/9da9df9b-68a6-49eb-9d4f-e080aa2eff7f)

0 files changed, 0 insertions, 0 deletions