feat: #3607135 Support for captcha element + requestValues on submitWebform
- Expose the captchaType on WebformElementCaptcha
- Introduce requestValues on submitWebform mutation to pass any additional request values for the submission. The captcha validators read the captcha response from request()->get(). The new requestValues argument allows for any additional values to be set (not just for captchas, but for other things as well)
Closes #3607135