scripting: Add js object <-> QRectF/QSizeF/QPointF conversion helpers

The js code contains code such as

    window.frameGeometry = {x: 42, y: 42, width: 100, height: 50};

However, QJSEngine doesn't know how to convert js object to QRect. For
that purpose, we need to register conversion functions.

So far, we kept registering converter functions only for integer based
geometry types, i.e. QRect, QSize and QPoint. In 5.26, Window was ported
to QRectF, QSizeF and QPointF, but the corresponding conversion helpers
were not added.

BUG: 459369