Refactor: scheduler: best practices when updating actions for ordering flags

Rename graph_update_action() to update_action_for_ordering_flags(), add a
doxygen block, improve comments, and use pcmk_is_set()/pcmk_any_flags_set()
where appropriate.

This drops the "node" function argument since it can be determined from the
other arguments, and uses order->type directly instead of creating a type
variable for it.