registerTutorialStep method
Return an unique global key and register this step
Implementation
GlobalKey<_ZwapTutorialOverlayWrapperState> registerTutorialStep(int stepNumber) {
if (log) _log('Registered focus key for step $stepNumber');
final GlobalKey<_ZwapTutorialOverlayWrapperState> _key = GlobalKey();
_tmpKeys[stepNumber] = _key;
return _key;
}