Fix #28740 demangle constructors in stack traces (A.A becomes new A).

runtime/vm/object.cc

Index: runtime/vm/object.cc
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index b012e5a80fe6bba680491c37853f7619fb627382..6225d594a2f2410c280c797c60909f7f9bed3158 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -7147,11 +7147,16 @@ RawString* Function::QualifiedName(NameVisibility name_visibility) const {
   }
   const Class& cls = Class::Handle(Owner());
   if (!cls.IsTopLevel()) {
-    result = String::Concat(Symbols::Dot(), result, Heap::kOld);
-    const String& cls_name = String::Handle(name_visibility == kScrubbedName
-                                                ? cls.ScrubbedName()
-                                                : cls.UserVisibleName());
-    result = String::Concat(cls_name, result, Heap::kOld);
+    if (kind() == RawFunction::kConstructor) {
+      result = String::Concat(Symbols::ConstructorStacktracePrefix(), result,
+                              Heap::kOld);
+    } else {
+      result = String::Concat(Symbols::Dot(), result, Heap::kOld);
+      const String& cls_name = String::Handle(name_visibility == kScrubbedName
+                                                  ? cls.ScrubbedName()
+                                                  : cls.UserVisibleName());
+      result = String::Concat(cls_name, result, Heap::kOld);
+    }
   }
   return result.raw();
 }