stylecontext: Deprecate regions

Regions are done in a very non-css way. They don't fit the DOM in that
they don't integrate into the CSS tree and they have very weird matching
behavior in selectors.

So I'm deprecating them now. GtkNotebook and GtkTreeview will continue
to use them and as long as they do, we can't remove the code for it.
But once those are ported it might be safe to remove the code as it will
clean up lots of places in the code by quite a bit.

gtk/gtkstylecontext.c

@@ -79,14 +79,18 @@
  * #GtkSettings:gtk-theme-name setting or a hierarchy change in the rendered
  * widget.
  *
- * # Style Classes and Regions # {#gtkstylecontext-classes}
+ * # Style Classes # {#gtkstylecontext-classes}
  *
  * Widgets can add style classes to their context, which can be used
  * to associate different styles by class
  * (see [Selectors][gtkcssprovider-selectors]).
  * Theme engines can also use style classes to vary their rendering.
  *
- * Widgets can also add regions with flags to their context.
+ * # Style Regions
+ *
+ * Widgets can also add regions with flags to their context. This feature is
+ * deprecated and will be removed in a future GTK+ update. Please use style
+ * classes instead.
  *
  * The regions used by GTK+ widgets are:
  *
@@ -1823,6 +1827,8 @@ gtk_style_context_list_classes (GtkStyleContext *context)
  *          itself with g_list_free() when you are done with it.
  *
  * Since: 3.0
+ *
+ * Deprecated: 3.14
  **/
 GList *
 gtk_style_context_list_regions (GtkStyleContext *context)
@@ -1902,6 +1908,8 @@ _gtk_style_context_check_region_name (const gchar *str)
  * and “-”, starting always with a lowercase letter.
  *
  * Since: 3.0
+ *
+ * Deprecated: 3.14
  **/
 void
 gtk_style_context_add_region (GtkStyleContext *context,
@@ -1943,6 +1951,8 @@ gtk_style_context_add_region (GtkStyleContext *context,
  * Removes a region from @context.
  *
  * Since: 3.0
+ *
+ * Deprecated: 3.14
  **/
 void
 gtk_style_context_remove_region (GtkStyleContext *context,
@@ -1986,6 +1996,8 @@ gtk_style_context_remove_region (GtkStyleContext *context,
  * Returns: %TRUE if region is defined
  *
  * Since: 3.0
+ *
+ * Deprecated: 3.14
  **/
 gboolean
 gtk_style_context_has_region (GtkStyleContext *context,