[HLSL][RootSignature] Audit RootSignatureParser diagnostic production (#147800)

This pr audits the diagnostics produced in `RootSignatureParser`
diagnostics.

First, it has been noted more than once that the current
`diag::err_hlsl_unexpected_end_of_params` is not direct and can be
misleading. For instance,
[here](#147350 (comment))
and
[here](#145827 (comment)).

This pr address this by removing this diagnostic and replacing it with a
more direct `diag::err_expected_either`. However, doing so removes the
nuance between the case where it is a missing comma and when it was an
invalid parameter.

Hence, we introduce the `diag::err_hlsl_invalid_token` for the latter
case, which does so in a direct way. Further, we can apply the same
diagnostic to the parsing of parameter values.

As part of this, we see that there was a test gap in testing the
diagnostics produced from `diag::err_expected_after` and for the parsing
of enum/flag values. As such, these are also addressed here to provide
sufficient unit/sema test coverage.

- Removes all uses of `diag::err_hlsl_unexpected_end_of_params` in
`RootSigantureParser`
- Introduce `diag::err_hlsl_invalid_token` to provide a direct
diagnostic
- In each of these cases, replace the diagnostic with either a
`diag::err_hlsl_invalid_token` or `diag::err_expected_either`
accordingly
- Update `HLSLRootSignatureParserTest` to account for diagnostic changes
- Increase test coverage of `HLSLRootSignatureParserTest` for enum/flag
diagnostics
- Increase test coverage of `RootSignatures-err` for enum/flag
diagnostics
- Small fix-up of the `diag::err_expected_after` and add test to
demonstrate usage

Resolves: #147799

Author: inbelic

clang/include/clang/Basic/DiagnosticParseKinds.td

@@ -1863,8 +1863,7 @@ def err_hlsl_virtual_inheritance
     : Error<"virtual inheritance is unsupported in HLSL">;
 
 // HLSL Root Signature Parser Diagnostics
-def err_hlsl_unexpected_end_of_params
-    : Error<"expected %0 to denote end of parameters, or, another valid parameter of %1">;
+def err_hlsl_invalid_token : Error<"invalid %select{parameter|value}0 of %1">;
 def err_hlsl_rootsig_repeat_param : Error<"specified the same parameter '%0' multiple times">;
 def err_hlsl_rootsig_missing_param : Error<"did not specify mandatory parameter '%0'">;
 def err_hlsl_number_literal_overflow : Error<

clang/include/clang/Parse/ParseHLSLRootSignature.h

@@ -100,7 +100,8 @@ class RootSignatureParser {
     std::optional<llvm::dxbc::RootDescriptorFlags> Flags;
   };
   std::optional<ParsedRootDescriptorParams>
-  parseRootDescriptorParams(RootSignatureToken::Kind RegType);
+  parseRootDescriptorParams(RootSignatureToken::Kind DescKind,
+                            RootSignatureToken::Kind RegType);
 
   struct ParsedClauseParams {
     std::optional<llvm::hlsl::rootsig::Register> Reg;
@@ -110,7 +111,8 @@ class RootSignatureParser {
     std::optional<llvm::dxbc::DescriptorRangeFlags> Flags;
   };
   std::optional<ParsedClauseParams>
-  parseDescriptorTableClauseParams(RootSignatureToken::Kind RegType);
+  parseDescriptorTableClauseParams(RootSignatureToken::Kind ClauseKind,
+                                   RootSignatureToken::Kind RegType);
 
   struct ParsedStaticSamplerParams {
     std::optional<llvm::hlsl::rootsig::Register> Reg;
@@ -135,13 +137,20 @@ class RootSignatureParser {
   std::optional<float> parseFloatParam();
 
   /// Parsing methods of various enums
-  std::optional<llvm::dxbc::ShaderVisibility> parseShaderVisibility();
-  std::optional<llvm::dxbc::SamplerFilter> parseSamplerFilter();
-  std::optional<llvm::dxbc::TextureAddressMode> parseTextureAddressMode();
-  std::optional<llvm::dxbc::ComparisonFunc> parseComparisonFunc();
-  std::optional<llvm::dxbc::StaticBorderColor> parseStaticBorderColor();
-  std::optional<llvm::dxbc::RootDescriptorFlags> parseRootDescriptorFlags();
-  std::optional<llvm::dxbc::DescriptorRangeFlags> parseDescriptorRangeFlags();
+  std::optional<llvm::dxbc::ShaderVisibility>
+  parseShaderVisibility(RootSignatureToken::Kind Context);
+  std::optional<llvm::dxbc::SamplerFilter>
+  parseSamplerFilter(RootSignatureToken::Kind Context);
+  std::optional<llvm::dxbc::TextureAddressMode>
+  parseTextureAddressMode(RootSignatureToken::Kind Context);
+  std::optional<llvm::dxbc::ComparisonFunc>
+  parseComparisonFunc(RootSignatureToken::Kind Context);
+  std::optional<llvm::dxbc::StaticBorderColor>
+  parseStaticBorderColor(RootSignatureToken::Kind Context);
+  std::optional<llvm::dxbc::RootDescriptorFlags>
+  parseRootDescriptorFlags(RootSignatureToken::Kind Context);
+  std::optional<llvm::dxbc::DescriptorRangeFlags>
+  parseDescriptorRangeFlags(RootSignatureToken::Kind Context);
 
   /// Use NumericLiteralParser to convert CurToken.NumSpelling into a unsigned
   /// 32-bit integer