tests: Test XML outputs
Load the outputs of the tests in Gtk.Builder and make sure they work. Some of them didn't and were fixed. One still needs to be fixed: property lookups sometimes require cast expressions, which aren't implemented yet.
Load the outputs of the tests in Gtk.Builder and make sure they work. Some of them didn't and were fixed. One still needs to be fixed: property lookups sometimes require cast expressions, which aren't implemented yet.