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.Common/Traits/Targetable.cs

@@ -11,6 +11,7 @@
 
 using System.Collections.Generic;
 using System.Linq;
+using OpenRA.Primitives;
 using OpenRA.Traits;
 
 namespace OpenRA.Mods.Common.Traits
@@ -19,8 +20,8 @@ namespace OpenRA.Mods.Common.Traits
 	public class TargetableInfo : ConditionalTraitInfo, ITargetableInfo
 	{
 		[Desc("Target type. Used for filtering (in)valid targets.")]
-		public readonly HashSet<string> TargetTypes = new HashSet<string>();
-		public HashSet<string> GetTargetTypes() { return TargetTypes; }
+		public readonly BitSet<TargetableType> TargetTypes;
+		public BitSet<TargetableType> GetTargetTypes() { return TargetTypes; }
 
 		public bool RequiresForceFire = false;
 
@@ -53,7 +54,7 @@ namespace OpenRA.Mods.Common.Traits
 			return cloaks.All(c => c.IsTraitDisabled || c.IsVisible(self, viewer.Owner));
 		}
 
-		public virtual HashSet<string> TargetTypes { get { return Info.TargetTypes; } }
+		public virtual BitSet<TargetableType> TargetTypes { get { return Info.TargetTypes; } }
 
 		public bool RequiresForceFire { get { return Info.RequiresForceFire; } }
 	}