Evaluate the rector/rector dev dependency

[TravisCarden]

• Part of Evaluate dev dependencies #78.

Dependency	rector/rector
Description	Automated refactoring for predefined code quality rules.
Value/justification	Medium High. Similar to PHPStan in terms of the kinds of issues it finds and fixes--largely type safety, unused code, and potential defect risks, etc. It has some overlap with PHPStan but also frequently finds things PHPStan doesn't. Here's an example of changes from an early run as it was incrementally enabled: 0e03219
Usage/popularity	Very High. Currently over 30M installs and 2K dependents on Packagist.
Security policy	None that I can find.
Maintainance	Very active. Responsive maintainers. Frequent, well-documented releases adhere to Semver.
Considerations	It has very thorough user documentation. Drupal Rector provides a precedent for its use in the Drupal community.

Dependency tree

$ composer info --tree rector/rector
rector/rector 0.18.6 Instant Upgrade and Automated Refactoring of any PHP code
├──php ^7.2|^8.0
└──phpstan/phpstan ^1.10.35
   └──php ^7.2|^8.0