feat(codegen): Adds InvalidateProperties (#616)

Adds invalidate properties to code genned fields.

Example:
```cs
[InvalidateProperties]
[EncodedInt]
private int _number; // Cliloc
```

Generates:
```cs
public int Number
{
    get => _number;
    set
    {
        if (value != _number)
        {
            _number = value;
            ((ISerializable)this).MarkDirty();
            InvalidateProperties();
        }
    }
}
```

Projects/Server/Serialization/InvalidatePropertiesAttribute.cs

@@ -0,0 +1,28 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2021 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: InvalidatePropertiesAttribute.cs                                *
+ *                                                                       *
+ * This program is free software: you can redistribute it and/or modify  *
+ * it under the terms of the GNU General Public License as published by  *
+ * the Free Software Foundation, either version 3 of the License, or     *
+ * (at your option) any later version.                                   *
+ *                                                                       *
+ * You should have received a copy of the GNU General Public License     *
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+ *************************************************************************/
+
+using System;
+
+namespace Server
+{
+    /// <summary>
+    /// Hints to the source generator that this field will execute an InvalidateProperties when the value is set
+    /// and the value is different from the current value.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.Field)]
+    public class InvalidatePropertiesAttribute : Attribute
+    {
+    }
+}