Refactor big_pipe module to remove dependencies on Ajax classes

Problem/Motivation

We intend to deprecate the Ajax API. The big_pipe module had Javascript dependencies removed in 📌 Refactor BigPipe to use HTMX Active . The following dependencies remain in PHP:

\Drupal\big_pipe\Render\BigPipe

• Drupal\Core\Ajax\AjaxResponse;
• Drupal\Core\Ajax\MessageCommand;
• Drupal\Core\Ajax\RedirectCommand;
• Drupal\Core\Ajax\ReplaceCommand;

Proposed resolution

Revisit the work set aside in MR 12295 which used tags to enclose the rendered placeholder markup. That MR was passing all tests but was lacking a better solution for messages.

If individual messages can be rendered via a solution in 🐛 AJAX MessageCommand markup and styling differs from Theme default Active or some other means, then messages can be sent in a very similar fashion to placeholder markup.

Remaining tasks

User interface changes

No UI for BigPipe

Introduced terminology

None

API changes

Internal changes only.

Data model changes

Internal changes only.

Release notes snippet