Drop size-based style classes when unmapped
Some widgets add a style class to reflect their state, e.g. HdyLeaflet
gives itself the folded
or unfolded
style classes, and HdyClamp
can give itself the small
, medium
or large
style classes. These widgets have none of these classes when they are created and gain them as their sizes are computed.
But we have an inconsistency: if a widget is unmapped it can't have a size, so these classes don't make sense anymore. We should remove them when unmapping these widgets.