GtkTextHandle: Better draw() implementation

Conceptually, text handles are boxes, whose content is a 'handle',
so draw background, frame and handle. With this, and the previous
commit, the cursor-handle theming in Adwaita now works as intended.

gtk/gtktexthandle.c

@@ -129,6 +129,8 @@ _gtk_text_handle_draw (GtkTextHandle         *handle,
                                  GTK_STYLE_CLASS_TOP);
 
   gtk_render_background (context, cr, 0, 0, width, height);
+  gtk_render_frame (context, cr, 0, 0, width, height);
+  gtk_render_handle (context, cr, 0, 0, width, height);
 
   gtk_style_context_restore (context);
   cairo_restore (cr);