[clang] [llvm] [HLSL][RootSignature] Add `hlsl-rootsig-ver` option to specify root signature version (PR #144813)

[Finn Plummer via llvm-commits]

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inbelic wrote:

Going through the commits 1 by 1 should be easier to read then from top to bottom of this diff.

https://github.com/llvm/llvm-project/pull/144813