It's getting harder and harder to find a dummy style property to use
here, so remove the test case since style properties should be going
away soon anyway.
And replaces its usages in GtkTextView/GtkStyleContext with a hard-coded
0.04 which was the default value for cursor-aspect-ratio. Also remove
the public gtk_draw_insertion_cursor which used draw_insertion_cursor
which in turn looked up cursor-aspect-ratio
When loading a nonexisting CSS file using
gtk_css_provider_load_from_file() or gtk_css_provider_load_from_path()
we would emit the error using a NULL scanner. Don't do that, because
we'll have a NULL section in that case and error handlers don't like
that.
Testcase attached.
https://bugzilla.redhat.com/show_bug.cgi?id=1277959
