Rewrite the implementations:

- Move the implementation to SemaTemplate.cpp where the typical CTAD
  implementation lives, thus no sepatate CTAD.h/.cpp;
- Rewrite the implementation, we leverage more on clang's template
  instantatiation mechanism to build the deduction guide, it
  implementation is simplier;
- Some enhancements on TreeTransform and TemplateInstantiator to allow
  running on BuildingDeductionGuides mode;
- Added more tests;

Author: hokein

clang/include/clang/Sema/Sema.h

@@ -10424,6 +10424,9 @@ class Sema final {
                       const MultiLevelTemplateArgumentList &TemplateArgs,
                       bool EvaluateConstraints = true);
 
+  bool SubstTemplateArgument(const TemplateArgumentLoc &Input,
+                             const MultiLevelTemplateArgumentList &TemplateArgs,
+                             TemplateArgumentLoc &Output);
   bool
   SubstTemplateArguments(ArrayRef<TemplateArgumentLoc> Args,
                          const MultiLevelTemplateArgumentList &TemplateArgs,

clang/lib/Sema/CMakeLists.txt

@@ -14,7 +14,6 @@ clang_tablegen(OpenCLBuiltins.inc -gen-clang-opencl-builtins
 
 add_clang_library(clangSema
   AnalysisBasedWarnings.cpp
-  CTAD.cpp
   CodeCompleteConsumer.cpp
   DeclSpec.cpp
   DelayedDiagnostic.cpp