Changed MiniYaml.NodesDict property into a method.

Method is now called ToDictionary.
- Cached a few invocations into locals which should prevent some redundant evaluation.
- Added ToDictionary overloads that take projection functions for the keys and elements, since several callsites were doing a subsequent Linq.ToDictionary call to get this.

OpenRA.Game/Graphics/Sequence.cs

@@ -33,7 +33,7 @@ namespace OpenRA.Graphics
 		{
 			var srcOverride = info.Value;
 			Name = name;
-			var d = info.NodesDict;
+			var d = info.ToDictionary();
 			var offset = float2.Zero;
 			var blendMode = BlendMode.Alpha;