reCaptcha should fallback to another Captcha

Problem/Motivation

If the user does not accept the reCaptcha cookie, the form is essentially disabled. A fallback to another captcha would be less coercive allowing the use to submit the form with say and image Captcha instead.

Steps to reproduce

enable and configure cookies, cookies reCaptcha, captcha, and reCaptcha modules. decline reCaptcha cookies.

Proposed resolution

provision for a fallback captcha.

(not clear if this would have to be in the Captcha module, or in both)