It was used to mark css properties that affect widgets with text, but it
caused unnecessary invalidations. E.g. 'color' was marked as
AFFECTS_TEXT but changing just the color of a label should not
automatically queue a resize, which is what the code in
gtk_widget_real_style_updated does.

Replace this flag with GTK_CSS_AFFECTS_TEXT_SIZE and
GTK_CSS_AFFECTS_TEXT_CLIP, which GtkWidget can use only if the widget
actually has text.

https://bugzilla.gnome.org/show_bug.cgi?id=791281