register method
Implementation
void register(HintTargetRegistration registration) {
final existing = _byId[registration.id];
if (existing != null && !identical(existing, registration)) {
final warning = "hintful: duplicate target id '${registration.id}'"
' — newest registration wins';
if (kDebugMode) debugPrint(warning);
onWarning?.call(warning);
}
_byId[registration.id] = registration;
_notifyChanged();
}