VideoCommon: Rework scissor handling

This increases accuracy, fixing the white rendering in Major Minor's Majestic March.  However, the hardware backends can only have one viewport and scissor rectangle at a time, while sometimes multiple are needed to accurately emulate what is happening.  If possible, this will need to be fixed later.

Source/Core/VideoCommon/VertexShaderManager.cpp

@@ -298,7 +298,7 @@ void VertexShaderManager::SetConstants()
     }
 
     dirty = true;
-    BPFunctions::SetViewport();
+    BPFunctions::SetScissorAndViewport();
   }
 
   if (bProjectionChanged || g_freelook_camera.GetController()->IsDirty())