Say why a brush cannot paint; paint at the layer's own resolution; Cancel and Apply only when an edit waits, scaled layers' scale (13.11)

src/UI/NativeLayerList.h

@@ -279,3 +279,6 @@ private:
     const QMimeData *m_dragData = nullptr;
     Qt::DropActions m_dragActions;
 };
+
+// The size on the canvas and, once scaled, how much.
+QString sizeLabel(const ImageLayer &layer);