[alternative] Use NodeVisitor for init attribute flag over global Node traverse

[samsonasik]

@peterfox per your feedback at #443 (comment)

This move to use NodeVisitor over global Node. Here the benefit and drawback:

Benefit:

• can reuse class constant attribute over rules if needed.

Drawback:

• The default config is included in sets, but if user just want to use some rule that require the attribute, user need to import the default config:

->withSets([
     __DIR__ . '/vendor/driftingly/rector-laravel/config/config.php'
])
->withRules([
     // the rule from this repo :)
]);

I've updated readme for it tho.

[samsonasik]

@GeniJaho @driftingly @peterfox ready for review/merge 👍