Function apply_scheduler_levels 

pub fn apply_scheduler_levels<C>(
    staged_held: &mut HashSet<C>,
    lmb_held: &mut bool,
    rmb_held: &mut bool,
    window_focused: &mut bool,
    sched: &Scheduler,
    code_for: impl Fn(PhysicalKey) -> Option<C>,
    keys_for: impl Fn(&C) -> Option<&'static [PhysicalKey]>,
)
where
    C: Eq + Hash + Clone,