fix: Removes broken OrderedHashSet and adds a simple OrderedSet (#1756)

> [!CAUTION]
> **BREAKING CHANGE**
> Removed `OrderdHashSet` and `PooledOrderedHashSet` due to bugs.

> [!NOTE]
> **Developer Note**
> The OrderedSet is not a full data structure. It is not particularly efficient. Pull Requests are welcome for a better implementation, especially if it ends up supporting `ISet<T>` and `IReadOnlySet<T>`

## Summary

The ordered hash set was buggy. It's kind of painful to implement, so for now, I added a simple `OrderedSet` to suffice for gumps. Please reach out if this causes disruption!

Projects/Server/Collections/OrderedSet.cs

@@ -0,0 +1,62 @@
+/*************************************************************************
+ * ModernUO                                                              *
+ * Copyright 2019-2024 - ModernUO Development Team                       *
+ * Email: hi@modernuo.com                                                *
+ * File: OrderedSet.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.Collections.Generic;
+using System.Runtime.CompilerServices;
+using System.Runtime.InteropServices;
+
+namespace Server.Collections;
+
+/// <summary>
+/// A data structure designed for scenarios where the order of insertion is important.
+/// Note: This is not particularly effecient.
+/// </summary>
+/// <typeparam name="T">The type of elements in the set.</typeparam>
+public class OrderedSet<T>
+{
+    private readonly Dictionary<T, int> _dictionary;
+    private readonly List<T> _list;
+
+    public OrderedSet(IEqualityComparer<T> comparer = null)
+    {
+        _dictionary = new Dictionary<T, int>(comparer);
+        _list = [];
+    }
+
+    public int Count => _dictionary.Count;
+
+    public int Add(T value)
+    {
+        ref var order = ref CollectionsMarshal.GetValueRefOrAddDefault(_dictionary, value, out var exists);
+        if (exists)
+        {
+            return order;
+        }
+
+        _list.Add(value);
+        return order = _list.Count - 1;
+    }
+
+    public bool Contains(T value) => _dictionary.ContainsKey(value);
+
+    public void Clear()
+    {
+        _dictionary.Clear();
+        _list.Clear();
+    }
+
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public List<T>.Enumerator GetEnumerator() => _list.GetEnumerator();
+}