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.Mods.Common/Widgets/ProductionTabsWidget.cs

@@ -196,7 +196,7 @@ namespace OpenRA.Mods.Common.Widgets
 			{
 				var allQueues = a.World.ActorsWithTrait<ProductionQueue>()
 					.Where(p => p.Actor.Owner == p.Actor.World.LocalPlayer && p.Actor.IsInWorld && p.Trait.Enabled)
-					.Select(p => p.Trait).ToArray();
+					.Select(p => p.Trait).ToList();
 
 				foreach (var g in Groups.Values)
 					g.Update(allQueues);