bottomToTop scrollOffset preservation

[elfredpagan]

Details

When using the bottomToTop layoutDirection, we should preserve scroll position relative to the bottom of the collection view whenever we change bounds.

Related Issue

Motivation and Context

How Has This Been Tested

Tested in the airbnb app

Types of changes

• [ ] Docs change / refactoring / dependency upgrade
• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING document.
• [ ] I have added tests to cover my changes.

[elfredpagan]

@bryankeller changes should be addressed now.