Using the symfony/json-streamer component on an object which contains a list of self (list<int, self>, self[]) generates invalid JSON.

This happens because the generated code does not yield a comma (,) for the first entry in the list and instead outputs an additional comma at the end of the list.

A class like:

class Dummy
{
    /** @var Dummy[] */
    public array $dummies = [];
}

Currently outputs invalid JSON:

{"dummies":[{"dummies":[]}{"dummies":[]},{"dummies":[]},]}

This PR fixes the above example to output valid JSON:

{"dummies":[{"dummies":[]},{"dummies":[]},{"dummies":[]}]}