Checked LINQ queries and collections for inefficiencies.

- Made Array.IndexOf available via extension method.
- Made ToHashSet extension method.
- Change collections queried often via Contains into sets.
- Avoid Count() extension if Count or Length property exist.
- Made Count() > 0 checks and variations calls to Any() instead.
- Don't call ToList/ToArray if there is no benefit to materializing the sequence.
- If the sequence does benefit from materialization, follow this general pattern:
  - Collection queried often via Contains use ToHashSet to speed up lookups.
  - Short lived variables use ToList. This is because ToArray requires an extra copy to output the final size.
  - Collections persisted into fields or for a long time use ToArray to minimize memory overhead.

OpenRA.Game/Scripting/ScriptContext.cs

@@ -80,7 +80,7 @@ namespace OpenRA.Scripting
 			// The 'this.' resolves the actual (subclass) type
 			var type = this.GetType();
 			var names = type.GetCustomAttributes<ScriptGlobalAttribute>(true);
-			if (names.Count() != 1)
+			if (names.Length != 1)
 				throw new InvalidOperationException("[LuaGlobal] attribute not found for global table '{0}'".F(type));
 
 			Name = names.First().Name;
@@ -242,13 +242,13 @@ namespace OpenRA.Scripting
 				runtime.Dispose();
 		}
 
-		static Type[] ExtractRequiredTypes(Type t)
+		static IEnumerable<Type> ExtractRequiredTypes(Type t)
 		{
 			// Returns the inner types of all the Requires<T> interfaces on this type
 			var outer = t.GetInterfaces()
 				.Where(i => i.IsGenericType && i.GetGenericTypeDefinition() == typeof(Requires<>));
 
-			return outer.SelectMany(i => i.GetGenericArguments()).ToArray();
+			return outer.SelectMany(i => i.GetGenericArguments());
 		}
 
 		static readonly object[] NoArguments = new object[0];