Convert all data object fields to JSON strings.

[noplanman]

?	!
Type	improvement
BC Break	no

Summary

Converts any objects that have been passed to request methods to a JSON string.

This makes it possible to pass native objects directly in requests, for example (using Request::setChatPermissions from Bot API 4.4):

Request::setChatPermissions([
    'chat_id'     => '<chat_id>',
    'permissions' => new ChatPermissions([
        'can_send_messages' => true,
        'can_send_polls'    => true,
        'can_change_info'   => true,
    ]),
]);

[jacklul]

Looks good 👍