Fix a crash when D&D a vector layer from one image to another

The patch does several things

1) Removes "application/x-krita-node" mimedata completely. It was
   used to pass Krita nodes between multiple instances of Krita. Since
   we don't support multiinstance runs anymore, these types should go.
   (they failed in multiple usecases anyway)

2) Implements a special KisDetachedShapesViewConverter converter class
   that is attached to KisShapeLayerCanvasBase, when it has no image
   attached (that was an exact cause of the crash). Now, when the
   vector layer is placed into a mime data, its converter is replaced
   with the detached one to no rely on KisImage (which is deleted at that
   moment)

BUG:456450