Boy this was hard.
To ease the pain of porting wireless-security to GTK4, add
a new WsFileChooserButton class that mimics the behavior of
a button that triggers a filechooser, as per the migration
guide suggests.
There were lots of GtkGrids, so the diff is particularly
horrendous. Sorry.
This needs serious testing before landing.
This has the side effect of allowing these pages to be shorter - the hidden
widgets forced the visible widgets to have a minimum height. If the old
behaviour is desired then this requires this to be fixed using a better
method.
