feat(ci): add scripts to quickly check and fix code styles

[bshaffer]

Now you can run both styles checkers with one line:

composer style-check
# > vendor/bin/php-tools cs-fixer googleapis/google-cloud-php
# > vendor/bin/phpcs --standard=phpcs-ruleset.xml -p

And if that fails you can fix it with another one-liner:

composer style-fix
# > vendor/bin/php-tools cs-fixer googleapis/google-cloud-php --flags ""
# > vendor/bin/phpcbf --standard=phpcs-ruleset.xml -p

And for consistency, you can also use composer phpstan as a shortcut to running dev/sh/static-analysis:

composer phpstan
# > dev/sh/static-analysis