get rid of container focus adjustments
Apart from focus handling being incredibly complex with all the different properties on
GtkWidget and the few vfuncs, we also have "different" focus handling for widgets and containers right now.
Specifically, we have
gtkcontainer.c which contains the code for
GtkContainer subclasses and
gtkwidget.c. The main difference of the container code is the handling of focus chains, which
GtkWidget does not support.