Avoid relying on LLM for markup in the content suggestions modal

We seem to be using JSON for responses throughout the AI project, so would suggest the same here. E.g.

Do not include any explanations, only provide a RFC8259 compliant JSON response following this format without deviation.
[
  {"suggestion": "First suggested text"},
  {"suggestion": "Second suggested text"},
]

I think this can be also in 1.2.x, as with update hook it is possible to change the system prompt.

I have changed the system prompt for content suggestions and created an update hook. In case the response from LLM is valid json, the suggestions are returned as structured HTML markup with twig template, if it is just a string, it is displayed in the modal dialog.

Since this was created as a follow up from https://www.drupal.org/project/ai/issues/3531588 ✨ Per-field ai_content_suggestions UX improvements Active , and both MRs will contain conflicts and adjustments that would be needed if either one is merged first, we'll include the changes from here, there. This way we dont have to make the same changes twice.

a.dmitriiev → closed merge request !698

bbruno → changed the visibility of the branch 3532137-avoid-relying-on to active.

bbruno → changed the visibility of the branch 3532137-avoid-relying-on to hidden.