fix: hidden horizontal-scroll flippers disabled by default

[robarbms]

Pull Request

📖 Description

If a horizontal-scroll element is rendered while hidden, it will calculate all of it's child nodes as 0px wide. This will cause the next flipper to be disabled by default. It will also make all of the scroll stops 0px.

This change will check that the last stop, which positioned against, is not 0 when hiding the next flipper. This will allow it to show the next flipper if it suspects that the horizontal-scroll was hidden when rendered. It will also verify that stops are not 0 and rerun HorizontalScroll.setStops() any time that the next and previous flippers are clicked.

🎫 Issues

https://github.com/microsoft/fast/issues/6261

👩‍💻 Reviewer Notes

📑 Test Plan

Built it out and tested in archive/fast-components

✅ Checklist

General

• [x] I have included a change request file using $ yarn change
• [ ] I have added tests for my changes.
• [x] I have tested my changes.
• [ ] I have updated the project documentation to reflect my changes.
• [x] I have read the CONTRIBUTING documentation and followed the standards for this project.

Component-specific

• [ ] I have added a new component
• [x] I have modified an existing component
• [ ] I have updated the definition file
• [ ] I have updated the configuration file

⏭ Next Steps