Introduce IMouseBounds and split/rework mouse rectangles.

The render bounds for an actor now include the area covered
by bibs, shadows, and any other widgets. In many cases this
area is much larger than we really want to consider for
tooltips and mouse selection.

An optional Margin is added to Selectable to support cases
like infantry, where we want the mouse area of the actor
to be larger than the drawn selection box.

OpenRA.Game/Traits/Player/FrozenActorLayer.cs

@@ -52,6 +52,9 @@ namespace OpenRA.Traits
 		public IRenderable[] Renderables = NoRenderables;
 		public Rectangle[] ScreenBounds = NoBounds;
 
+		// TODO: Replace this with an int2[] polygon
+		public Rectangle MouseBounds = Rectangle.Empty;
+
 		static readonly IRenderable[] NoRenderables = new IRenderable[0];
 		static readonly Rectangle[] NoBounds = new Rectangle[0];
 
@@ -298,7 +301,7 @@ namespace OpenRA.Traits
 
 		public virtual IEnumerable<IRenderable> Render(Actor self, WorldRenderer wr)
 		{
-			return world.ScreenMap.FrozenActorsInBox(owner, wr.Viewport.TopLeft, wr.Viewport.BottomRight)
+			return world.ScreenMap.RenderableFrozenActorsInBox(owner, wr.Viewport.TopLeft, wr.Viewport.BottomRight)
 				.Where(f => f.Visible)
 				.SelectMany(ff => ff.Render(wr));
 		}