[clang] [llvm] [NFC][HLSL][DirectX] Let `HLSLRootSignature` reuse the `dxbc` defined enums (PR #145986)

[Sarah Spall via llvm-commits]

================
@@ -404,7 +417,7 @@ TEST_F(ParseHLSLRootSignatureTest, ValidSamplerFlagsTest) {
   ASSERT_TRUE(std::holds_alternative<DescriptorTableClause>(Elem));
   ASSERT_EQ(std::get<DescriptorTableClause>(Elem).Type, ClauseType::Sampler);
   ASSERT_EQ(std::get<DescriptorTableClause>(Elem).Flags,
-            DescriptorRangeFlags::ValidSamplerFlags);
----------------
spall wrote:

This change seems surprising, but I didn't know the previous code and what ValidSamplerFlags represents.

https://github.com/llvm/llvm-project/pull/145986