Function style::animation::start_transitions_if_applicable

pub fn start_transitions_if_applicable(
    context: &SharedStyleContext<'_>,
    old_style: &ComputedValues,
    new_style: &Arc<ComputedValues>,
    animation_state: &mut ElementAnimationSet
) -> PropertyDeclarationIdSet

Kick off any new transitions for this node and return all of the properties that are transitioning. This is at the end of calculating style for a single node.