Issue #3107872 by bnjmnm, lauriii: Decouple Classy libraries from Seven

...Drupal/KernelTests/Core/Theme/ConfirmClassyCopiesTest.php

...KernelTests/Core/Theme/ThemeNotUsingClassyLibraryTest.php

core/themes/seven/css/classy/components/action-links.css

core/themes/seven/css/classy/components/book-navigation.css

core/themes/seven/css/classy/components/breadcrumb.css

core/themes/seven/css/classy/components/button.css

...themes/seven/css/classy/components/collapse-processed.css

core/themes/seven/css/classy/components/container-inline.css

core/themes/seven/css/classy/components/dropbutton.css

core/themes/seven/css/classy/components/exposed-filters.css

core/themes/seven/css/classy/components/field.css

core/themes/seven/css/classy/components/file.css

core/themes/seven/css/classy/components/form.css

core/themes/seven/css/classy/components/forum.css

core/themes/seven/css/classy/components/icons.css

core/themes/seven/css/classy/components/image-widget.css

core/themes/seven/css/classy/components/indented.css

core/themes/seven/css/classy/components/inline-form.css

core/themes/seven/css/classy/components/item-list.css

core/themes/seven/css/classy/components/link.css