[cxx-interop] Fix missing APIs and tests after rebase.

 * Update tests that relied on old behavior.
 * Use mangleCXXName instead of mangleCXXCtor.
 * Call VisitCXXRecordDecl not VisitRecordDecl from
 VisitClassTemplateSpecializationDecl. This allows template constructors
 to be imported and called correctly.

Author: zoecarver

lib/ClangImporter/ClangImporter.cpp

@@ -3590,7 +3590,9 @@ void ClangImporter::getMangledName(raw_ostream &os,
     Impl.Mangler.reset(Impl.getClangASTContext().createMangleContext());
 
   if (auto ctor = dyn_cast<clang::CXXConstructorDecl>(clangDecl)) {
-    Impl.Mangler->mangleCXXCtor(ctor, clang::Ctor_Complete, os);
+    auto ctorGlobalDecl = clang::GlobalDecl(ctor,
+                                            clang::CXXCtorType::Ctor_Complete);
+    Impl.Mangler->mangleCXXName(ctorGlobalDecl, os);
   } else {
     Impl.Mangler->mangleName(clangDecl, os);
   }

lib/ClangImporter/ImportDecl.cpp

@@ -1241,6 +1241,10 @@ synthesizeStructDefaultConstructorBody(AbstractFunctionDecl *afd,
   ASTContext &ctx = constructor->getASTContext();
   auto structDecl = static_cast<StructDecl *>(context);
 
+  // We should call into C++ constructors directly.
+  assert(!isa<clang::CXXRecordDecl>(structDecl->getClangDecl()) &&
+         "Should not synthesize a C++ object constructor.");
+
   // Use a builtin to produce a zero initializer, and assign it to self.
 
   // Construct the left-hand reference to self.
@@ -3558,7 +3562,7 @@ namespace {
       Impl.getClangSema().InstantiateClassTemplateSpecializationMembers(
           def->getLocation(), def, clang::TSK_ExplicitInstantiationDefinition);
 
-      return VisitRecordDecl(def);
+      return VisitCXXRecordDecl(def);
     }
 
     Decl *VisitClassTemplatePartialSpecializationDecl(