Add static class helper for converting values

[pionl]

Sometimes we have value from different data source (like laravel form request) and we want to ensure that the type is correct.

For this we need only nullable values.

``php
Value::toInt($value);
Value::toString($value);
Value::toRequiredString($value);
Value::toBool($value);
Value::toArray($value);
Value::toFloat($value);

We want to reuse the basic `GetValue` logic for it.