- gimp_container_tree_view_prepend_toggle_cell_renderer() to
  gimp_container_tree_view_add_toggle_cell()

- gimp_container_tree_view_prepend_cell_renderer() to
  gimp_container_tree_view_add_renderer_cell()

because "prepend" is an implementation detail, "renderer" is obsolete,
and in the second case it's not "cell renderer" but really a "renderer
cell".