Commit working beta version of semgrep-merge-tool
Among other things, this change set:
- Establishes a proper composer.json and composer.lock
- Adds the mediawiki phpcs rules
- Add a .gitignore
- Adds a config.example.php file as the standard, global state config
- Adds the util/SMTCli.php script for various app setup operations (largely repo cloning and yaml config file generation)
Bug: T307962