setMix method
Implementation
void setMix(String fromName, String toName, double duration) {
final Animation? from = skeletonData.findAnimation(fromName);
if (from == null) throw StateError('Animation not found: $fromName');
final Animation? to = skeletonData.findAnimation(toName);
if (to == null) throw StateError('Animation not found: $toName');
setMixWith(from, to, duration);
}