Mount and Clone issue also showcase view issue with IntrinsicHeight

[nirajbpant]

Describe the bug
There is an issue about mount/unmount when you wrap certain index of a listview.builder with showcase widget and assign the first/selected index with a globalkey and try to scroll the listview.

There is also an issue when there is a dynamic rendering of widget using IntrinsicHeight and clone methods.

To Reproduce
Steps to reproduce the behavior:

1. Implement showcase view with unique key binded to first index item of the array.
2. Implement startshowcaseview and provide it with the unique globalkey.
3. Scroll down to the listview.
4. See error

Screenshots
https://imgur.com/a/dFZ6Lv5

Smartphone (please complete the following information):

• Device: Iphone xs, Android phones and emulator.