10 files declare their use of Tags in Zircon Profile 8.0

EntityAutocomplete.php in core/lib/Drupal/Core/Entity/Element/EntityAutocomplete.php

Contains \Drupal\Core\Entity\Element\EntityAutocomplete.

EntityAutocompleteController.php in core/modules/system/src/Controller/EntityAutocompleteController.php

Contains \Drupal\system\Controller\EntityAutocompleteController.

EntityAutocompleteMatcher.php in core/lib/Drupal/Core/Entity/EntityAutocompleteMatcher.php

Contains \Drupal\Core\Entity\EntityAutocompleteMatcher.

EntityAutocompleteTest.php in core/modules/system/src/Tests/Entity/EntityAutocompleteTest.php

Contains \Drupal\system\Tests\Entity\EntityAutocompleteTest.

TagsTest.php in core/tests/Drupal/Tests/Core/Common/TagsTest.php

Contains \Drupal\Tests\Core\Common\TagsTest.

taxonomy.module in core/modules/taxonomy/taxonomy.module

Enables the organization of content into categories.

TermTest.php in core/modules/taxonomy/src/Tests/TermTest.php

Contains \Drupal\taxonomy\Tests\TermTest.

UnpublishByKeywordComment.php in core/modules/comment/src/Plugin/Action/UnpublishByKeywordComment.php

Contains \Drupal\comment\Plugin\Action\UnpublishByKeywordComment.

UnpublishByKeywordNode.php in core/modules/node/src/Plugin/Action/UnpublishByKeywordNode.php

Contains \Drupal\node\Plugin\Action\UnpublishByKeywordNode.

ViewExecutable.php in core/modules/views/src/ViewExecutable.php

Contains \Drupal\views\ViewExecutable.