Issue #3084814 by JeroenT, catch, lauriii, dww, Gábor Hojtsy, xjm, quietone: Deprecate Seven theme

(cherry picked from commit 81593d83cc)

core/themes/seven/seven.info.yml

@@ -13,6 +13,8 @@
 # changes.
 name: Seven
 type: theme
+lifecycle: deprecated
+lifecycle_link: https://www.drupal.org/node/3223395#s-seven
 base theme: false
 description: 'The default administration theme for Drupal 8 was designed with clean lines, simple blocks, and sans-serif font to emphasize the tools and tasks at hand.'
 alt text: 'Default administration theme for Drupal 8 with simple blocks and clean lines.'

core/themes/seven/tests/src/Functional/SevenLayoutBuilderTest.php

@@ -8,6 +8,7 @@ use Drupal\Tests\BrowserTestBase;
  * Tests the Seven theme.
  *
  * @group seven
+ * @group legacy
  */
 class SevenLayoutBuilderTest extends BrowserTestBase {