fix: Optimize OrderedHashSet and introduce more high perf collections (#679)

* Optimizes OrderedHashSet using the learnings here: https://github.com/dotnet/runtime/issues/10050
* Removes ValueCollection since it was a relic from the conversion of the OrderedDictionary
* Centralizes throw strings.
* Adds pooled ordered hash set (but doesn't use it)

Closes #448

Projects/Server/Collections/CollectionHelpers.cs

@@ -14,14 +14,16 @@
  *************************************************************************/
 
 using System.Collections.Generic;
+using System.Runtime.CompilerServices;
 
 namespace Server.Collections
 {
     public static class CollectionHelpers
     {
+        [MethodImpl(MethodImplOptions.AggressiveInlining)]
         public static void AddNotNull<T>(this ICollection<T> coll, T t) where T : class
         {
-            if (t != default)
+            if (t != null)
             {
                 coll.Add(t);
             }