[clang][ASTDump] Dump value of structural TemplateArguments

`TemplateArgument::ArgKind::StructuralValue` was introduced in
#78041

The AST dump for such template arguments would yield the following:
```
|-ClassTemplateSpecializationDecl
  `- TemplateArgument
```

With this patch we would dump as:
```
|-ClassTemplateSpecializationDecl
  `-TemplateArgument structural '1.000000e+00'
```

Author: Michael137

clang/include/clang/AST/TextNodeDumper.h

@@ -253,6 +253,7 @@ class TextNodeDumper
   void VisitTemplateExpansionTemplateArgument(const TemplateArgument &TA);
   void VisitExpressionTemplateArgument(const TemplateArgument &TA);
   void VisitPackTemplateArgument(const TemplateArgument &TA);
+  void VisitStructuralValueTemplateArgument(const TemplateArgument &TA);
 
   void VisitIfStmt(const IfStmt *Node);
   void VisitSwitchStmt(const SwitchStmt *Node);

clang/lib/AST/TextNodeDumper.cpp

@@ -1226,6 +1226,11 @@ void TextNodeDumper::VisitIntegralTemplateArgument(const TemplateArgument &TA) {
   dumpTemplateArgument(TA);
 }
 
+void TextNodeDumper::VisitStructuralValueTemplateArgument(const TemplateArgument &TA) {
+  OS << " structural";
+  dumpTemplateArgument(TA);
+}
+
 void TextNodeDumper::dumpTemplateName(TemplateName TN, StringRef Label) {
   AddChild(Label, [=] {
     {