Expose GtkEntry icons as child accessibles of a GtkEntry, and provide actions to simulate clicking them. Also, refactor the a11y children test slightly to add a test. https://bugzilla.gnome.org/show_bug.cgi?id=686347
Updated test/a11y/entries.ui to include a new GtkEntry with 'visibility' set to FALSE, and update expectations. https://bugzilla.gnome.org/show_bug.cgi?id=681591