This pr adds the equivalent validation of `llvm.loop` metadata that is
[done in
DXC](8f21027f2a/lib/DxilValidation/DxilValidation.cpp (L3010)).
This is done as follows:
- Add `llvm.loop` to the metadata allow-list in `DXILTranslateMetadata`
- Iterate through all `llvm.loop` metadata nodes and strip all
incompatible ones
- Raise an error for ill-formed nodes that are compatible with DXIL
Resolves: https://github.com/llvm/llvm-project/issues/137387
- Changed `DXILTranslateMetadata::translateMetadata()` to consume DXIL
Metadata Analysis information. Subsumed into `DXILTranslateMetedata.cpp`
the functionality in `DXILMetadata.*` files - that are hence deleted.
- Changed `DXILPrepare` pass to consume DXIL Metadata Analysis
information.
- Renamed `ModuleMetadataInfo::ShaderStage` to
`ModuleMetadataInfo::ShaderProfile` to better convey what it represents.
- Updated `unknown` target shader stage specification in triples of a
couple of tests.
- Added new tests for additional verification of `DXILTranslateMetadata`
pass functionality.
