Summary:
## Changes in this pull request
This PR adds a new feed view controller demo to the IGListKit example app, showcasing how to implement a social media feed with IGListKit. The demo features infinite scrolling with pagination, post deletion, and interactive elements. Also, I've improved the UI testing infrastructure by adding helper methods for more reliable tests across different device types. The new helpers make the tests more resilient when dealing with iPad split views and ensure elements are properly visible before interacting with them.
### Checklist
- [X] All tests pass. Demo project builds and runs.
- [X] I added tests, an experiment, or detailed why my change isn't tested.
- [X] I added an entry to the `CHANGELOG.md` for any breaking changes, enhancements, or bug fixes.
- [x] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/main/.github/CONTRIBUTING.md)
Pull Request resolved: https://github.com/Instagram/IGListKit/pull/1629
Reviewed By: fabiomassimo
Differential Revision: D77482204
Pulled By: TimOliver
fbshipit-source-id: 44ac86ed253e8452388aad50a1ed05bc6f3a31ab
Summary: Introduces a compositional layout example that leverages section controller methods to determine layout.
Differential Revision: D71402637
fbshipit-source-id: 1179abf13157fb5cb78c8a9086718d1216fb4276
