Weird Vertical Scroll Indicator Top

[jparksecurity]

We can see the top of vertical scroll indicator moves when a keyboard comes up and goes down.

https://user-images.githubusercontent.com/14362029/106378947-1f713f80-636e-11eb-8388-61339dfe867a.mov

Reproducible: https://snack.expo.io/@horaeng/4d0721 (different from the video)

The step is below:

1. click one of TextInput
2. look at the top of vertical scroll indicator as the keyboard comes up
3. dismiss the keyboard by clicking outside of the text input
4. look at the top of vertical scroll indicator as the keyboard goes down.

Expected behavior: no change at the top of the indicator.

Possible solution: It seems indicator offset gets changed somehow. If so, don't change the offset.