[gtk/wip/antoniof/dont-hard-code-properties-if-buildable] paned: Don't override properties when buildable

[António Fernandes <antoniof src gnome org>]

commit 850565b8e857cc266ed649d786bbef8d307c2695
Author: António Fernandes <antoniojpfernandes gmail com>
Date:   Sat Jan 1 21:41:07 2022 +0000

    paned: Don't override properties when buildable
    
    We set GtkPaned:{shrink,resize}-{start,end}-child when adding children
    as buildable.
    
    This overrides whatever value the UI definition had set for the properties.
    Even if not  set explicitly, the properties have a default value anyway.
    
    This fixes an issue I found while porting nautilus to GTK 4, as the
    start child was shrinkable even though :shrink-start-child was set
    to FALSE in the .ui file.