ViewProviderAttachExtension::extensionMergeOverlayIcons() calls
AttachExtension::positionBySupport() which will always touch the
extended object. This may cause recomputation problems, e.g a datum
that is always touched, because normal recomputation trigger tree
view update by a timer, tree view refreshes the icon, datum gets
touched again.
AttachableObjects are desired in multiple occasions, and the current AttachableObject is not flexible enough to handle all cases. Hence the code is portet to an extension, which gives the needed flexibility.
