Add a proper fake on the facade

[RVxLab]

Instead of needing to manually mock the display and verify calls, it's nice to be able to just call HCaptcha::fake() and have it automatically set some reasonable defaults.

This will require the introduction of a contract:

interface HCaptchaContract
{
    public function display(array $attributes = []): string;

    public function displayWidget(array $attributes = []): string;

    public function displaySubmit(string $formIdentifier, string $buttonText = 'submit', array $attributes = []): string;

    public function renderJs(?string $lang = null, bool $hasCallback = false, string $onLoadClass = 'onloadCallBack'): string;

    public function verifyResponse(string $response, ?string $clientIp = null): bool;

    public function verifyRequest(Request $request): bool;

    public function getJsLink(?string $lang = null, bool $hasCallback = false, string $onLoadClass = 'onloadCallBack'): string;
}

For the fake, any of the display methods can return an input with any value, so it can be rendered and form validation will succeed.

The getJsLink method can just return an empty string, that's not really important here.

The verify methods should return true by default with the option to mock that call as needed by means of a shouldVerify(bool) or a successfullyVerifies() and failsVerification() pair.