isInitialized top-level property Null safety

1. Figma2flutter
2. figma2flutter
3. isInitialized property

figma2flutter library

1. Classes
2. Elem
3. Event
4. Properties
5. elementInstances
6. eventSubscriptions
7. images
8. isInitialized
9. isWeb
10. navigatorKey
11. screenClasses
12. simpleEvents
13. Functions
14. addComponentItems
15. getApp
16. getComponentState
17. getComponentText
18. getElementsByName
19. getFirstElementByName
20. getLocationSearch
21. getWidgetHashCode
22. getWidgetInstanceByName
23. openAppPage
24. parseItem
25. parseItems
26. removeAllComponentEvents
27. removeComponentEvent
28. replaceComponentItems
29. setComponentImageUrl
30. setComponentItems
31. setComponentProperties
32. setComponentState
33. setComponentText
34. setDropdownValues
35. subscribeToComponentEvent
36. subscribeToEvent
37. subscribeToEventOnce
38. triggerComponentEvent
39. triggerEvent