Remove deprecations in ajax.js

Good cleanup

Let's take care of the todo in this issue too and add a deprecation warning. See https://www.drupal.org/node/3082634

   * @todo Add deprecation warning after it is possible. For more information
   *   see: https://www.drupal.org/project/drupal/issues/2973400

code looks good, some linting issues left

Fixing linting issues.

The MR is now against 11.x.

There are two issues for this work, the other is #3301204: Properly deprecate ajax.js methods. Although the other is older this one has an MR so, lets continue work here. Also, adding credir

There are dozens of JavaScript test failures here, but from a quick scan, it looks like this deprecation might be all of them:

2x: Javascript Deprecation: The Drupal.theme.ajaxWrapperNewContent is
    deprecated in drupal:8.6.0 and is removed from drupal:11.0.0. See
    https://www.drupal.org/node/2940704
        2x in ViewsWizardTest::testCreateViewWizard from
    Drupal\Tests\views_ui\FunctionalJavascript
---- Drupal\Tests\workspaces\FunctionalJavascript\WorkspaceToolbarIntegration

The issue is this code, which triggers the deprecation on every Ajax insert:

      // For backward compatibility, in some cases a wrapper will be added. This
      // behavior will be removed before Drupal 9.0.0. If different behavior is
      // needed, the theme functions can be overridden.
      // @see https://www.drupal.org/node/2940704
      $newContent = Drupal.theme(
        'ajaxWrapperNewContent',
        $newContent,
        ajax,
        response,
      );

I don't think the current deprecation is going to help anyway. The change notice tells you to override the method if you want to change the behaviour; if you do this then the deprecation we add here won't be fired - in fact it's only fired if you *don't* override it, which is the wrong way round?

Maybe what we need to do is:

1. Remove Drupal.theme.ajaxWrapperNewContent and Drupal.theme.ajaxWrapperMultipleRootElements
2. In Drupal.AjaxCommand.insert if Drupal.theme.ajaxWrapperNewContent exists then:
1. Issue a deprecation
2. If Drupal.theme.ajaxWrapperMultipleRootElements exists then issue another deprecation
3. If Drupal.theme.ajaxWrapperMultipleRootElements doesn't exist, define it (because the first theme function might call it)
4. Call it as before
3. Else if Drupal.theme.ajaxWrapperMultipleRootElements exists then issue a deprecation and use it?
4. Otherwise: just hardcode the wrapper in the multiple elements case? It's not clear from the change record what we will do if there are still more than one root-level element returned.

Or, decide this is too complicated, and just drop it all from Drupal 11 without any deprecations, as we deprecated this several years ago and the code mentions removal from Drupal 9 etc, so in the event anyone was overriding this they have had plenty of notice anyway.

Or, decide this is too complicated, and just drop it all from Drupal 11 without any deprecations, as we deprecated this several years ago and the code mentions removal from Drupal 9 etc, so in the event anyone was overriding this they have had plenty of notice anyway.

This is very appealing and I think we should do it. We can always try to improve the 10.x deprecations if it turns out to be a problem, but it's also quite possible no-one is relying on it.

It's still not clear what to do about the multiple root elements case; this is the breaking change.

@lauriii in #736066-357: ajax.js insert command sometimes wraps content in a div, potentially producing invalid HTML and other bugs:

The support for effects with multiple root elements is meant to be temporary. I also proposed that we give a warning for any users that would be affected by this logic, but we don't have a way to do that until #2962344: [policy, no patch] Document how to handle deprecations in JavaScript has been resolve.

So if we only add the div when there's multiple root elements and an effect, the bug would be fixed in most cases, and there wouldn't be any known breaking changes for existing sites.

However, we still haven't triggered that warning, and there may be users relying on the div wrapper around multiple elements.

So, new proposal:

• In 10.3.x trigger a deprecation in Drupal.theme.ajaxWrapperNewContent only when the .length > 1 condition is true. If you were overriding this as per the change record, we assume you knew what you were doing; either you were adding divs back everywhere (but we told you this was going away), or you were overriding the multiple divs wrapper, and your code will be obsolete soon.
• In 11.x remove all this code and drop the multiple div wrapper.

Rebased MR!3784 against 10.3.x and implemented #23.

Also opened MR!7670 for the removal in Drupal 11.

Some tests failing on both MRs.

Seems tests need deeper rework.

The merge requests need to be updated to the latest changes on their respective branches.

We need align with
https://www.drupal.org/project/drupal/issues/3238870

The deprecation was updated so this code would be removed in Drupal 12.0.

Rebased. Please review!

Appears like a good removal.

Discussed this with @longwave. We both think it's OK to go ahead and remove this without the tricky deprecation layer, 8.6 was a very long time ago.

However there are at least two test failures in the latest pipeline that look very related (AJAX test + one performance test).

Javascript errors appear to be valid to the change.

Forgot about this one and was doing deprecation removals in #3575462: Remove deprecations from themes and misc and hitting the same test failures.

Fixed 1 test but still not sure about testBlockFilter

Still don't have a fix but the bug is that filtering on layout builder doesn't work at all now

I’d like to propose we don’t do this lol. It breaks layout builder filtering so may be a fair assumption it’ll break a contrib module. But reason I’m proposing we skip is because htmx will replace Ajax and we can eventually delete this file

Not finished for beta so moving to next major.