gtk4: gtk_box_pack_start()/end() porting

[Murray Cumming <murrayc murrayc com>]

gtk4's gtk_box_pack_start() and gtk_box_pack_end() now no longer have
the expand and fill parameters that are in GTK+3:
https://developer.gnome.org/gtk3/stable/GtkBox.html#gtk-box-pack-start
these are the commits that removed them:
https://git.gnome.org/browse/gtk+/commit/?id=c92b7d4224b9cef1d08373fcc2
8f7fbd96c64e6d
https://git.gnome.org/browse/gtk+/commit/?id=5729ea7744c2a41ae8fb833db6
690a6aa5ad7a84

But, based on some experiments, it doesn't seem obvious to me exactly
how to replace these by setting halign, valign, hexpand or vexpand.
Could someone please add a mapping of the old fill/expand combinations
to the new halign/valign/hexpand/vexpand properties to the migrating
guide?
https://git.gnome.org/browse/gtk+/tree/docs/reference/gtk/migrating-3to
4.xml

There are only 4 possible fill/expand combinations, only 3 of which
ever made sense, so this should be doable.

-- 
Murray Cumming
murrayc murrayc com
www.murrayc.com