Update the following dependencies:
* php-unit
* mediawiki-codesniffer
Use specific dependencies.
Fix issues highlighted by new rules in mediawiki-codesniffer
Additional changes in this PR include,
* Added composer.json
* Refactored the folder structure.
* Added editorconfig.
* Added PHPCS and formatted existing code.
* Changes to use a single license - GPL-2.0-or-later
* ESLint related fixes
Bug: T218639