Function reduce_motion 

pub fn reduce_motion() -> bool

Whether motion should be reduced (docs/accessibility.md): the user’s system setting (Toolkit::reduce_motion), or a launch that forced it (DAY_REDUCE_MOTION=1, and day launch --fast, whose fast mode is this setting forced on). Day already applies every finite animation at its destination under it and keeps only indeterminate motion; this read is for the motion an app drives itself, such as a day::frame simulation or a decorative loop, which the app opts down. Reactive: a closure reading it re-runs when the setting flips.