Emit accessible change signals after setting the
new selection limits. This was broken in
commit f6bedd0d5e4c8f7b, and showed up as broken
accessibility tests.

Strip down GtkContainer

See merge request GNOME/gtk!1722

This was only living in gtkcontainer.c for historic
reasons. Move it closer to where it belongs, and
rename it from 'idle' to 'layout', since it is
really about the layout phase of the frame clock,
nowadays.

Remove remnants of child properties from the
documentation. They no longer exist.

Move the set_focus_child vfunc from GtkContainer
to GtkWidget. This removes the last focus functionality
from GtkContainer.

Update the two users.

gtkpopover: Set GTK grab on autohide popovers

Closes #2446

See merge request GNOME/gtk!1729

These popovers handle clicks outside the widget, and expect input
to be routed through it when it is shown. This pretty much matches
the characteristics of GTK grabs, and setting one up will ensure
the cancellation of event controllers that were active at the time
of showing the popover.

Closes: https://gitlab.gnome.org/GNOME/gtk/-/issues/2446

Docs work

See merge request GNOME/gtk!1727