Create a small library for ObjectFactory, since it is a dependency of ObjectCache/{T146257}
* [x] Create repo, bootstrap with [mediawiki/tools/cookiecutter-library](https://phabricator.wikimedia.org/diffusion/MCCL/)
* [ ] Set up Jenkins jobs:
- [x] composer-test for patch and submit pipeline (use `composer-test-package` template in zuul/layout)
- [ ] publish Doxygen
- [ ] publish Coverage
* [x] Initial import of code, tests, and documentation.
- [x] Use PSR-4 autoloader
- [x] Use "Wikimedia" namespace
- [x] phpcs
- [x] phpunit
* [ ] Publish composer package to Packagist, under `wikimedia/`.
* [ ] Add documentation link to https://doc.wikimedia.org.
* [ ] Ensure Gerrit-Phabricator replication.
* [x] Ensure Gerrit-GitHub replication.
* [x] Create documentation page on mediawiki.org. <https://www.mediawiki.org/wiki/ObjectFactory>