feat: introduce JSON normalizer

[romm]

The normalizer is able to normalize a data structure to JSON without using the native json_encode() function.

Using the normalizer instead of the native json_encode() function offers some benefits:

• Values will be recursively normalized using the default transformations
• All registered transformers will be applied to the data before it is formatted
• The JSON can be streamed to a PHP resource in a memory-efficient way

Basic usage:

namespace My\App;

$normalizer = (new \CuyZ\Valinor\MapperBuilder())
    ->normalizer(\CuyZ\Valinor\Normalizer\Format::json());

$userAsJson = $normalizer->normalize(
    new \My\App\User(
        name: 'John Doe',
        age: 42,
        country: new \My\App\Country(
            name: 'France',
            code: 'FR',
        ),
    )
);

// `$userAsJson` is a valid JSON string representing the data:
// {"name":"John Doe","age":42,"country":{"name":"France","code":"FR"}}

By default, the JSON normalizer will return a JSON string representing the data it was given. Instead of getting a string, it is possible to stream the JSON data to a PHP resource:

$file = fopen('path/to/some_file.json', 'w');

$normalizer = (new \CuyZ\Valinor\MapperBuilder())
    ->normalizer(\CuyZ\Valinor\Normalizer\Format::json())
    ->streamTo($file);

$normalizer->normalize(/* … */);

// The file now contains the JSON data

Another benefit of streaming the data to a PHP resource is that it may be more memory-efficient when using generators — for instance when querying a database:

// In this example, we assume that the result of the query below is a
// generator, every entry will be yielded one by one, instead of
// everything being loaded in memory at once.
$users = $database->execute('SELECT * FROM users');

$file = fopen('path/to/some_file.json', 'w');

$normalizer = (new \CuyZ\Valinor\MapperBuilder())
    ->normalizer(\CuyZ\Valinor\Normalizer\Format::json())
    ->streamTo($file);

// Even if there are thousands of users, memory usage will be kept low
// when writing JSON into the file.
$normalizer->normalize($users);