Use a BitSet for representing target types.

- Rename Bits<T> to BitSet<T>.
- Implement set based helpers for BitSet<T>.
- When representing TargetTypes of ITargetable in various traits, use a BitSet<TargetableType> instead of HashSet<string> for better performance & reduced memory usage.
- Fix FieldLoader to trim input values when generating a BitSet<T>.
- Require T in BitSet<T> and BitSetAllocator<T> to be a class since it's just a marker value. This allows the JIT to instantiate generic code for these classes once, as they don't benefit from specialized code for T. (Typically JITs will generate shared code for all reference types, and unique code for every value type encountered).

OpenRA.Mods.Cnc/Traits/Infiltration/InfiltrateForCash.cs

@@ -13,6 +13,7 @@ using System;
 using System.Collections.Generic;
 using OpenRA.Mods.Common.Effects;
 using OpenRA.Mods.Common.Traits;
+using OpenRA.Primitives;
 using OpenRA.Traits;
 
 namespace OpenRA.Mods.Cnc.Traits
@@ -20,7 +21,7 @@ namespace OpenRA.Mods.Cnc.Traits
 	[Desc("This structure can be infiltrated causing funds to be stolen.")]
 	class InfiltrateForCashInfo : ITraitInfo
 	{
-		public readonly HashSet<string> Types = new HashSet<string>();
+		public readonly BitSet<TargetableType> Types;
 
 		[Desc("Percentage of the victim's resources that will be stolen.")]
 		public readonly int Percentage = 100;
@@ -47,7 +48,7 @@ namespace OpenRA.Mods.Cnc.Traits
 
 		public InfiltrateForCash(InfiltrateForCashInfo info) { this.info = info; }
 
-		void INotifyInfiltrated.Infiltrated(Actor self, Actor infiltrator, HashSet<string> types)
+		void INotifyInfiltrated.Infiltrated(Actor self, Actor infiltrator, BitSet<TargetableType> types)
 		{
 			if (!info.Types.Overlaps(types))
 				return;