We were looking at the wrong class names here, we need
to look at the owner type to match against our list.
This fixes problems where gtk-builder-tool simplify
inadvertedly loses hexpand or vexpand settings, messing
up layout, as recently happend in gtk4-widget-factory.
Rewrite the builder-tool simplify command to have
a full parse tree around, and perform simplifications
on that tree. This lets us rewrite GtkStack and turn
child properties into child meta objects.
