[HLSL][RootSignature] `HLSLRootSignatureParser` should initialize default `flags` values based on version

[inbelic]

When adding RootSignatureVersion to the compiler options, it was forgotten to also update setDefaultFlags here, to set the default values of RootDescriptorFlags and DescriptorRangeFlags dependent on the version.

This requires an update to RootSignatureParser to be given the version and initialize accordingly.

AC:

• Update RootSignatureParser to have a Version member
• Use this version member to correctly invoke setDefaultFlags
• Update setDefaultFlags to initialize the flags correctly from the updated specs

[llvmbot]

@llvm/issue-subscribers-clang-frontend

Author: Finn Plummer (inbelic)

When adding `RootSignatureVersion` to the compiler options, it was forgotten to also update `setDefaultFlags` [here](https://github.com/llvm/llvm-project/blob/b413bea4355e51e3f3ff248b7d62b4d5d712c743/llvm/include/llvm/Frontend/HLSL/HLSLRootSignature.h#L172), to set the default values of `RootDescriptorFlags` and `DescriptorRangeFlags` dependent on the version.

This requires an update to RootSignatureParser to be given the version and initialize accordingly.

AC:

• Update RootSignatureParser to have a Version member
• Use this version member to correctly invoke setDefaultFlags
• Update setDefaultFlags to initialize the flags correctly from the updated specs