[docs] Add 'Since: 2.16' tag to GtkEntryIconPosition
[docs] Add 'Since: 2.16' tag to GtkEntryIconPosition

Signed-off-by: Javier Jardón <d9e631309e5549cc595b71faddf6ad547c795ffa@gnome.org>
(cherry picked from commit 972e75e8b0f463386e495ac095b7c6e5cbff8e61)

Distrotech/gtk,johne53/MB3Gtk-2,Distrotech/gtk,Unity-Technologies/gtk,Unity-Technologies/gtk,johne53/MB3Gtk-2,Unity-Technologies/gtk,johne53/MB3Gtk-2,Distrotech/gtk,Distrotech/gtk,johne53/MB3Gtk-2,johne53/MB3Gtk-2,Unity-Technologies/gtk,Unity-Technologies/gtk,Distrotech/gtk