VideoCommon: Better logic op invert approximation

Source/Core/VideoCommon/RenderState.h

@@ -109,6 +109,8 @@ union BlendingState
   // HACK: Replaces logical operations with blend operations.
   // Will not be bit-correct, and in some cases not even remotely in the same ballpark.
   void ApproximateLogicOpWithBlending();
+  bool LogicOpApproximationIsExact();
+  bool LogicOpApproximationWantsShaderHelp();
 
   BlendingState() = default;
   BlendingState(const BlendingState&) = default;