fix(Android): prevent sheet footer from flickering on sheet sliding

[kkafar]

Description

Previous implementation of sheetTopWhileDragging relied on linear interpolation. Due to numeric errors in floating point division sometimes the footer was +- 1 pixel up/down from the accurate position, resulting in 1px flickering / "dancing".

This PR changes the way sheet top is computed to making use of the parent screen top property, whenever possible.

Changes

• Add test dedicated to formsheet
• "Stabilize" footer

Test code and steps to reproduce

Added dedicated test TestFormSheet.

Checklist

• [ ] Included code example that can be used to test this change
• [ ] Updated TS types
• [ ] Updated documentation:
  • [ ] https://github.com/software-mansion/react-native-screens/blob/main/guides/GUIDE_FOR_LIBRARY_AUTHORS.md
  • [ ] https://github.com/software-mansion/react-native-screens/blob/main/native-stack/README.md
  • [ ] https://github.com/software-mansion/react-native-screens/blob/main/src/types.tsx
  • [ ] https://github.com/software-mansion/react-native-screens/blob/main/src/native-stack/types.tsx
• [ ] Ensured that CI passes