Container spacing does not adapt to style

The default spacing of child items inside containers is 0 px for positioners and 5 px for layouts. However, those values should adapt to the chosen style. For example, the default spacing in the Qt Widget Fusion theme is 6 px, as defined in QCommonStyle [1]. Microsoft's Universal style guidelines require all spacing to be multiples of 4 px [2], and the default spacing is 12 px [3]. The required spacing can be set manually of course, but this is not a solution for platform-independent applications.

[1] https://github.com/qt/qtbase/blob/dev/src/widgets/styles/qcommonstyle.cpp#L4782
[2] https://docs.microsoft.com/en-us/windows/uwp/design/basics/design-and-ui-intro#multiples-of-four
[3] https://github.com/microsoft/microsoft-ui-xaml/issues/82#:~:text=Default%20Spacing