Set DXIL version to 1.9 for SM6.9 release#8063

alsepkow wants to merge 2 commits intomicrosoft:release-1.9.2602microsoft/DirectXShaderCompiler:release-1.9.2602from

alsepkow:user/alsepkow/DecrementDXILVersionTo19alsepkow/DirectXShaderCompiler:user/alsepkow/DecrementDXILVersionTo19Copy head branch name to clipboard