[NFC][RootSignature] Move RootSignature util functions (#142491)

`HLSLRootSignature.h` was originally created to hold the struct
definitions of an `llvm::hlsl::rootsig::RootElement` and some helper
functions for it.

However, there many users of the structs that don't require any of the
helper methods. This requires us to link the `FrontendHLSL` library,
where we otherwise wouldn't need to.

For instance:
- This [revert](https://github.com/llvm/llvm-project/pull/142005) was
required as it requires linking to the unrequired `FrontendHLSL` library
- As part of the change required here:
https://github.com/llvm/llvm-project/issues/126557. We will want to add
an `HLSLRootSignatureVersion` enum. Ideally this could live with the
root signature struct defs, but we don't want to link the helper objects
into `clang/Basic/TargetOptions.h`

This change allows the struct definitions to be kept in a single header
file and to then have the `FrontendHLSL` library only be linked when
required.

0 files changed, 0 insertions, 0 deletions