[onPageScroll] nativeEvent.position is always 0

## Environment

` "react-native-pager-view": "^5.1.2" `
```
System:
OS: macOS 11.2.3
CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
Memory: 458.95 MB / 16.00 GB
Shell: 5.8 - /bin/zsh
Binaries:
Node: 12.19.0 - /usr/local/bin/node
Yarn: 1.22.5 - ~/.yarn/bin/yarn
npm: 7.7.5 - /usr/local/bin/npm
Watchman: 4.9.0 - /usr/local/bin/watchman
Managers:
CocoaPods: 1.10.1 - /usr/local/bin/pod
SDKs:
iOS SDK:
Platforms: iOS 14.4, DriverKit 20.2, macOS 11.1, tvOS 14.3, watchOS 7.2
Android SDK:
API Levels: 21, 23, 25, 26, 27, 28, 29
Build Tools: 23.0.1, 26.0.1, 26.0.2, 27.0.3, 28.0.3, 29.0.2
System Images: android-30 | Google APIs Intel x86 Atom
Android NDK: Not Found
IDEs:
Android Studio: 4.1 AI-201.8743.12.41.7199119
Xcode: 12.4/12D4e - /usr/bin/xcodebuild
Languages:
Java: 1.8.0_212 - /usr/bin/javac
npmPackages:
@react-native-community/cli: Not Found
react: ^17.0.2 => 17.0.2
react-native: ^0.64.0 => 0.64.0
react-native-macos: Not Found
npmGlobalPackages:
*react-native*: Not Found
```
## Description

the `position ` value of `onPageScroll` never change when page scroll finished


## Reproducible Demo