Splitter positions are not preserved in 3D edit view when 3D scene changes

If there are 2 or more 3D scenes in the QML document (i.e. 2 View3D elements), each 3D scene can have separate split preset in use, but if user resizes the splits, the resized positions are not remembered when active 3D scene changes.

The splitter positions should be included in the stored toolstate for each scene just like the selected split preset.