[AST] Print the "aggregate" for aggregate deduction guide decl. (#84018)

I found this is useful for debugging purpose to identify different kind
of deduction guide decl.

Author: hokein

clang/include/clang/AST/TextNodeDumper.h

@@ -352,6 +352,7 @@ class TextNodeDumper
   void VisitEnumConstantDecl(const EnumConstantDecl *D);
   void VisitIndirectFieldDecl(const IndirectFieldDecl *D);
   void VisitFunctionDecl(const FunctionDecl *D);
+  void VisitCXXDeductionGuideDecl(const CXXDeductionGuideDecl *D);
   void VisitFieldDecl(const FieldDecl *D);
   void VisitVarDecl(const VarDecl *D);
   void VisitBindingDecl(const BindingDecl *D);

clang/lib/AST/TextNodeDumper.cpp

@@ -1990,6 +1990,19 @@ void TextNodeDumper::VisitFunctionDecl(const FunctionDecl *D) {
   }
 }
 
+void TextNodeDumper::VisitCXXDeductionGuideDecl(
+    const CXXDeductionGuideDecl *D) {
+  VisitFunctionDecl(D);
+  switch (D->getDeductionCandidateKind()) {
+  case DeductionCandidate::Normal:
+  case DeductionCandidate::Copy:
+    return;
+  case DeductionCandidate::Aggregate:
+    OS << " aggregate ";
+    break;
+  }
+}
+
 void TextNodeDumper::VisitLifetimeExtendedTemporaryDecl(
     const LifetimeExtendedTemporaryDecl *D) {
   OS << " extended by ";

clang/test/SemaTemplate/deduction-guide.cpp

@@ -239,3 +239,12 @@ F s(0);
 // CHECK: |-InjectedClassNameType {{.*}} 'F<>' dependent
 // CHECK: | `-CXXRecord {{.*}} 'F'
 // CHECK: `-TemplateTypeParmType {{.*}} 'type-parameter-0-1' dependent depth 0 index 1
+
+template<typename T>
+struct G { T t; };
+
+G g = {1};
+// CHECK-LABEL: Dumping <deduction guide for G>:
+// CHECK: FunctionTemplateDecl
+// CHECK: |-CXXDeductionGuideDecl {{.*}} implicit <deduction guide for G> 'auto (T) -> G<T>' aggregate
+// CHECK: `-CXXDeductionGuideDecl {{.*}} implicit used <deduction guide for G> 'auto (int) -> G<int>' implicit_instantiation aggregate