Add new JSONThrowOnError tool

[wata727]

PHP 7.3 makes it to easy to handle json_* function errors easily.
Previously, these function didn't throw an exception when an error occurred. But now, it throws JsonException if passed JSON_THROW_ON_ERROR as a option. This is a better way to handle errors.

Before

json_decode("{");
if (json_last_error() !== JSON_ERROR_NONE) {
    echo "An error occurred";
}

After

try {
    json_decode("{", false, 512, JSON_THROW_ON_ERROR);
} catch (JsonException $exn) {
    echo "An error occurred";
}

Reference

https://secure.php.net/manual/en/function.json-decode.php
https://secure.php.net/manual/en/function.json-encode.php