[HLSL][RootSignature] Add support for `Qstrip_rootsignature` compiler flag

[inbelic]

This issue tracks implementing the DXC Qstrip_rootsignature compiler option.

The behaviour should follow the specification here.

AC:

• Implement the Qstrip_rootsignature driver option in clang-dxc
• Implement mdx-rootsignature-strip driver option in clang and cc1
• Update DXContianerGlobals to get access to the flag value and omit addRootSignature