Fix issue with race-condition in SkiaDrawView on iOS

[chrfalch]

On iOS the process of removing and unregistering a SkiaView is a bit more complicated than on Android, since the iOS RCTViewManager does not have a notification for a view removal. This causes a memory leak and we need to track adding/removing the SkiaView by using the willMoveToWindow on the wrapping UIView. This causes some issues with the implementation of the RNSkDrawView not being available when we create/remove the view (ex. in navigation transitions). In addition all of this can cause a race condition where the view is removed while it has a pending draw request that will be executed after the view was removed.

We need to solve a few things here

• Implement correct tracking of view add/remove using the willMoveToWindow method
• Refactor some of the RNSk code to support adding removing an implementation view without removing callbacks etc
• Refactor how we track removal and draw requests to support this scheme