Improve performance of calling ICustomTypeDescriptor.GetProperties

Src/Newtonsoft.Json/Linq/JObject.cs

@@ -744,13 +744,15 @@ namespace Newtonsoft.Json.Linq
 
         PropertyDescriptorCollection ICustomTypeDescriptor.GetProperties(Attribute[] attributes)
         {
-            PropertyDescriptorCollection descriptors = new PropertyDescriptorCollection(null);
-
+            var propertiesArray = new PropertyDescriptor[Count];
+            var i = 0;
             foreach (KeyValuePair<string, JToken?> propertyValue in this)
             {
-                descriptors.Add(new JPropertyDescriptor(propertyValue.Key));
+                propertiesArray[i] = new JPropertyDescriptor(propertyValue.Key);
+                i++;
             }
 
+            var descriptors = new PropertyDescriptorCollection(propertiesArray);
             return descriptors;
         }