SPM number10 (#1487)
Summary:
## Changes in this pull request
A better version of https://github.com/Instagram/IGListKit/issues/1465 =)
- SPM support with script-based generations.
- added macOS Catalyst support
### Generate SPM layout
1. From **project's root** run:
`bash scripts/generate_spm_sources_layout.sh`
2. Commit Changes
Repeat those steps each time you delete/add the project's files. **Make sure** to have this CI step which will check that `generate_spm_sources_layout.sh` is not broken.
Issue fixed: https://github.com/Instagram/IGListKit/issues/1368 #1406
### Checklist
- [ ] All tests pass. Demo project builds and runs.
- [ ] I added tests, an experiment, or detailed why my change isn't tested.
- [ ] I added an entry to the `CHANGELOG.md` for any breaking changes, enhancements, or bug fixes.
- [ ] I have reviewed the [contributing guide](https://github.com/Instagram/IGListKit/blob/master/.github/CONTRIBUTING.md)
Pull Request resolved: https://github.com/Instagram/IGListKit/pull/1487
Reviewed By: DimaVartanian, candance
Differential Revision: D30428297
Pulled By: lorixx
fbshipit-source-id: 655291ff03445dec9b0b8cd97916f0c88207e9a7
