Add BindingSerializer interface

[webmozart]

The interface BindingSerializer should be implemented which converts Bindings from and to JSON. This interface can be implemented to support custom Binding classes in puli.json.

namespace Puli\Manager\Api\Discovery;

interface BindingSerializer
{
    /**
     * @param  Binding
     * @return stdClass
     * @throws SerializationFailedException
     */
    public function serializeBinding(Binding $binding);

    /**
     * @param  stdClass
     * @return Binding
     * @throws UnserializationFailedException
     */
    public function unserializeBinding(stdClass $json);

    /**
     * @param  Binding
     * @return bool
     */
    public function acceptsBinding(Binding $binding);

    /**
     * @param  stdClass
     * @return bool
     */
    public function acceptsJson(stdClass $json);
}

It should be possible to define serializers in puli.json:

{
    "binding-serializers": [
        "Vendor\\Namespace\\ServiceBindingSerializer"
    ]
}

Each "bindings" entry in puli.json is passed to all known serializers in order to be unserialized. On the reverse, each Binding stored in a puli.json is passed to all known serializers in order to be serialized.