Please add mode for QWidgets to render layout indicators

This is a feature request for Qt Widgets module, not Qt Dedigner, but the interface did not seem to offer low level libraries as a "project".

When adding widgets to layouts programmatically, sometimes the layout renders in unexpected ways e.g. gaps/alignment issues. I find this happens mostly when using QGridLayout.

Please add something like

    QWidget :: setRenderLayoutHints (bool)

to enable a render mode in which the widget will render indicators of how the layout is working. For example, for QGridLayout this would render an overlay of grid lines.