SPM number10 (Instagram#1487)

Summary:
## Changes in this pull request

 A better version of Instagram#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: Instagram#1368 Instagram#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: Instagram#1487

Reviewed By: candance

Differential Revision: D25562739

Pulled By: lorixx

fbshipit-source-id: eb4f9e82e6b4842aae71585e0c1377c13cf21196

CHANGELOG.md

@@ -61,6 +61,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 
 ### Enhancements
 
+- Added [Mac Catalyst](https://developer.apple.com/mac-catalyst/) support. [Petro Rovenskyy](https://github.com/3a4oT/) 
+
 - Added `shouldSelectItemAtIndex:` to `IGListSectionController` . [dirtmelon](https://github.com/dirtmelon)
 
 - Introduce `IGListSwiftKit`, with Swift refinements for `dequeueReusableCellOfClass` methods. [Koen Punt](https://github.com/koenpunt) [(#1388)](https://github.com/Instagram/IGListKit/pull/1388).
@@ -73,6 +75,8 @@ The changelog for `IGListKit`. Also see the [releases](https://github.com/instag
 
 - Small performance improvement by replacing `NSSet` with `NSArray` during the data update to avoid unnecessary hashing, especially when dealing with lots of large objects with non trivial hashes. [Maxime Ollivier](https://github.com/maxolls) (tbd)
 
+- Repaired Swift Package Manager support. [Petro Rovenskyy](https://github.com/3a4oT/)
+
 - Lazy initialize the `-emptyViewForListAdapter:` [Maxime Ollivier](https://github.com/maxolls) (tbd)
 
 - Updated  `IGListAdapterUpdater` to be safer, more performant, and better organized! [Maxime Ollivier](https://github.com/maxolls) (tbd)

Examples/Examples-iOS/Podfile.lock

@@ -25,4 +25,4 @@ SPEC CHECKSUMS:
 
 PODFILE CHECKSUM: a9a6bbfc859f2bc942afe333e906138bc8c8f559
 
-COCOAPODS: 1.10.1
+COCOAPODS: 1.8.4

Examples/Examples-macOS/Podfile.lock

@@ -13,4 +13,4 @@ SPEC CHECKSUMS:
 
 PODFILE CHECKSUM: a5e65f00463ec091d58ee2241126ab30f6d2ee69
 
-COCOAPODS: 1.9.3
+COCOAPODS: 1.8.4