fix content offset adjustment for bounds changing

[jinxiao-zang]

Details

For the bottomToTop layout, the y offset adjustment max(currentCollectionView.bounds.height - newBounds.height + contentInset.bottom, 0) is not right. we should not involve the contentInset.bottom. The iOS system will help adjust the yOffset when new bounds exceed the boundary. It means we should check if newBounds.maxY < currentCollectionView.contentSize.height + contentInset.bottom as well.

Motivation and Context

We are building an messaging screen for Airbnb and I find this issue causes the message cells jumping when typing indicator hide and show.

How Has This Been Tested

I built a small sample to test this case. Before this change: The cells move up every time the bounds changed. After the change: The cells keep bottom spacing the same.

Before	After

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

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

[jinxiao-zang]

@brynbodayle @bryankeller PTAL!

[bryankeller]

Thanks @jinxiao-zang !