image captcha form element, missing refresh button.

Problem/Motivation

Currently, when using image_captcha/Image captcha type, it works perfectly fine inside added captcha points. But if we would like to use it inside a form, the refresh button is missing.

The reason is the following:

If we render the image captcha inside a captcha point, we first render the generel captcha data with our image_captcha data given to the captcha.html.twig. Once this is done, we use "image_captcha_element_info_alter" in our image_captcha module to post process our form and add the refresh button, to the form.

Unfortunately, this post-processing won't take place if we insert a captcha form element inside a form via '#type' => 'captcha' and therefore the refresh button is missing.

Steps to reproduce

Add:

    $form['test'] = [
      '#type' => 'captcha',
      '#captcha_type' => 'image_captcha/Image',
      '#captcha_admin_mode' => TRUE,
    ];

Inside a test form and check the output.

Proposed resolution

Implement something like "$captcha['post_process']" inside "hook_captcha_captcha" to let submodules register form postprocessing inside their custom captcha's "hook_captcha_captcha".

Remaining tasks

User interface changes

API changes

Data model changes