6 files declare their use of BreadcrumbBuilderInterface in Zircon Profile 8

BookBreadcrumbBuilder.php in core/modules/book/src/BookBreadcrumbBuilder.php

Contains \Drupal\book\BookBreadcrumbBuilder.

CommentBreadcrumbBuilder.php in core/modules/comment/src/CommentBreadcrumbBuilder.php

Contains \Drupal\comment\CommentBreadcrumbBuilder.

ForumBreadcrumbBuilderBase.php in core/modules/forum/src/Breadcrumb/ForumBreadcrumbBuilderBase.php

Contains \Drupal\forum\Breadcrumb\ForumBreadcrumbBuilderBase.

PathBasedBreadcrumbBuilder.php in core/modules/system/src/PathBasedBreadcrumbBuilder.php

Contains \Drupal\system\PathBasedBreadcrumbBuilder.

SystemBreadcrumbBlock.php in core/modules/system/src/Plugin/Block/SystemBreadcrumbBlock.php

Contains \Drupal\system\Plugin\Block\SystemBreadcrumbBlock.

TermBreadcrumbBuilder.php in core/modules/taxonomy/src/TermBreadcrumbBuilder.php

Contains \Drupal\taxonomy\TermBreadcrumbBuilder.