Incomplete functional conversion for NodeCacheTagsTest

Problem/Motivation

Looking at some test results, I wondered why telling run-tests.sh --types PHPUnit-Functional yielded a test that was based on Drupal\system\Tests\Cache\PageCacheTagsTestBase.

It turns out that the inheritance goes like this:

Drupal\Tests\node\Functional\NodeCacheTagsTest inherits from
Drupal\system\Tests\Entity\EntityWithUriCacheTagsTestBase which inherits from
Drupal\system\Tests\Entity\EntityCacheTagsTestBase.

There are two of those lowest ones:
Drupal\system\Tests\Entity\EntityCacheTagsTestBase and
Drupal\Tests\system\Functional\Entity\EntityCacheTagsTestBase.

And it turns out that:
Drupal\Tests\system\Functional\Entity\EntityCacheTagsTestBase inherits from
Drupal\system\Tests\Cache\PageCacheTagsTestBase (the simpletest one).

So basically there's a heirarchy of PHPUnit functional entity tests that inherit from WebTestBase.

Proposed resolution

Straighten it out.

Remaining tasks

User interface changes

API changes

Data model changes