builder-tool: Rewrite GtkBox
GtkBox currently is not rewritten with gtk4-builder-tool simplify --3to4
which results in warnings about leftover packing properties. This PR rewrites expand/fill properties on GtkBox to hexpand/halign/vexpand/valign on the child widget. Also rewrites GtkVBox/GtkHBox to GtkBox by setting the orientation property. A unit test was added for all of these changes.