Qt Designer: Add functionality to morph box layouts to QSplitter

QSplitters may be seen as a type of box layouts (i.e., QHBoxLayout and QVBoxLayout) that lets the user control the size of child widgets.  Therefore, when designing a form, the designer may want to try out how a design feels if the user is able to fiddle around with the size.   Currently, the only way that QtDesigner lets designers add widgets to a QSplitter is to select widgets and lay them out with a QSplitter (select widgets > right click on the selection > "Lay out" > "Lay out horizontally/vertically on a QSplitter").   Box layouts can already be morphed into other container types.  It would be very useful if Qt Designer let users select a QHBoxLayout/QVBoxlayout with two widgets and morph it into a QSplitter.--