New ITREE_FOREACH macro

New ITREE_FOREACH macro

* src/itree.h (interval_tree_iter_start): Adjust type.
(interval_tree_nodes): Delete declaration.
(ITREE_FOREACH, ITREE_FOREACH_ABORT, ITREE_FOREACH_NARROW): New macros.

* src/itree.c (interval_tree_contains, interval_tree_insert_gap):
Use the new ITREE_FOREACH macro.
(interval_tree_nodes): Delete function.
(interval_tree_iter_start): Return the iterator.
(interval_generator_next, interval_tree_destroy):
Don't accept a NULL arg any more.

* src/xdisp.c (load_overlay_strings, strings_with_newlines):
* src/textprop.c (get_char_property_and_overlay):
* src/buffer.c (copy_overlays, delete_all_overlays)
(set_overlays_multibyte, swap_buffer_overlays, overlays_in)
(next_overlay_change, previous_overlay_change, overlay_touches_p)
(overlay_strings, Foverlay_lists, report_overlay_modification)
(evaporate_overlays): Use the new ITREE_FOREACH macro.

* src/buffer.h (buffer_overlay_iter_start1)
(buffer_overlay_iter_start, buffer_overlay_iter_next)
(buffer_overlay_iter_finish, buffer_overlay_iter_narrow):
Delete declarations.