Release notes:
https://gitlab.freedesktop.org/wlroots/wlroots/-/releases/0.17.0

The following things were affected/added:
+ Update git submodule path to point to new repository
+ The output mode change event was removed in favor of the general
  output commit event. Remove the mode handler code instead of
  adapting to the changes, as there may be better ways to handle it.
  (https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/3911).
+ Use the wlr_scene_output_layout helper, which sets various things up
  that were implicilty done before.
  https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/4318
+ Since the backend no longer changes the ouput mode behind our code's
  back, we handle listen to the `request_state` event to have the
  previous behavior.
  https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/2693
+ Use the wlr_output_state event to atomically update the output state
  upon initialization.
+ Change where the xdg map events are stored:
  https://gitlab.freedesktop.org/wlroots/wlroots/-/merge_requests/4043