from static method
If data field is null, the return is null.
index must be a positive base-1 integer.
Implementation
static IndexedKeyframe? from({
required Keyframe? data,
required int index,
required bool isLast,
required bool newThisFrame,
}) {
if (data == null) return null;
assert(index > 0, "Keyframe index expected a positive, base-1 integer.");
return IndexedKeyframe._(data, index, isLast, newThisFrame);
}