Update remaining tests using Classy to use Starterkit

Self-assigning to work on this. I'll start with 10.1.x and we'll figure out how to backport it as needed.

Okay. The only remaining core test which contains defaultTheme = 'classy' is \Drupal\FunctionalTests\Theme\ClassyTest. That should clearly be moved into the contrib project, so I'll update the meta-issue.

Nice.

Assigning to @xjm for review per prior out-of-band discussion.

There are several test themes that have base theme: classy. Those uses need to be refactored as well as they're just as much a barrier to removing Classy.

Re-assigning to myself to make that change and see what breaks. If it turns out to cause a tsunami of complexity, I'd vote we do that in another stable-blocking follow-up.

Those remaining failures are fixed now (at least on my machine). Reassigning to @bnjmnm for review.

Boo, I forgot to deal with tests that install Classy using the theme installer. Maddening. Reassigning to work on that.

Okay, over to you now, @bnjmnm. I've addressed every test that mentions Classy in its code, and deleted a few cases/tests which will no longer be relevant when Classy is removed from core.

There's an open thread in Gitlab that I'm fine with as the test still checks for the same thing: is-active status. @phenaproxima spent a while looking for an explanation for the difference, but I'm going to RTBC this as I don't believe the need to change the test reflects anything beyond the fact that Classy and Starterkit aren't identical, and the change is very similar to the hundreds of changes made to tests switching from Classy to Stark as their default theme. (I would point out the two tests where that is happening, but Gitlab is currently down)

A committer is certainly welcome to push back and insist on full justification for the change, so I wanted to be sure this RTBC comes with confirmation that @phenaproxima and myself aren't 100% why those changes work, but do not feel they introduce any problems.

Alright, Gitlab is back
The two tests with changes that needed to be made to work with Starterkit and seem fine, but there isn't a conclusive explanation as what makes Classy & Starterkit different are:
core/modules/system/tests/src/Functional/Menu/LocalTasksTest.php
core/modules/views/tests/src/Functional/Plugin/DisplayPageWebTest.php

Small changes compare to switching to Stark but wanna make that disclosure full.

A few more nits + one more MR thread.

1. There are test dependencies on Classy in testing_install_profile_dependencies.info.yml testing_install_profile_all_dependencies.info.yml that should work fine switched to starterkit.
2. core/modules/ckeditor/tests/src/FunctionalJavascript/MediaTest.php references a Classy template that I assume it no longer Classy
   

       if ($media_embed_enabled) {
           // The preview rendering, which in this test will use Classy's
           // media.html.twig template, will fail without the CSRF token/header.
           // @see ::testEmbeddedMediaPreviewWithCsrfToken()
   

Hiding out-of-date patch from #14.

Alright I've read through this many times lets switch this to RTBC 🍿

Can someone move credit over from https://www.drupal.org/project/drupal/issues/3112548 where work was done to change it to stark.