Move interface IBlendState to own file

src/BizHawk.Bizware.BizwareGL/IBlendState.cs

@@ -0,0 +1,4 @@
+namespace BizHawk.Bizware.BizwareGL
+{
+	public interface IBlendState {}
+}

src/BizHawk.Bizware.BizwareGL/RenderStates.cs

@@ -1,7 +1,5 @@
 namespace BizHawk.Bizware.BizwareGL
 {
-	public interface IBlendState { }
-
 	/// <summary>
 	/// An IBlendState token that just caches all the args needed to create a blend state
 	/// </summary>