[x] Migrate DataModel, DataModelServices, DataModelSerialization, WBInternalSerialization to Wikibase.git packages
[x] Add patches to other Wikibase extensions to make them depend on Wikibase
[x] Add a patch to Wikibase that depends on the vendor patch
[x] Create a patch removing these packages from `mediawiki/vendor`
[x] Remove the packages from `composer.json`
[] ~~Add CI to create standalone git repos for these libraries and then alter the packagist configuration to read from these~~
[] ~~Mark the current GitHub repos as deprecated (and maybe archive them).~~
[] Ensure credentials are in place and each push action runs
[] Move (De)Serializer factory to the correct place and remove hacks to load them
[] Check PHPUnit Tests
[] Lib Hooks
[] phpunit.xml
[] phan config
Note: More info in `Wikibase/lib/packages/README.md`