Issue #2955842 by andypost, zrpnr, bnjmnm, alexpott, gapple: Deprecate classList library

core/core.libraries.yml

@@ -21,6 +21,7 @@ classList:
     gpl-compatible: true
   js:
     assets/vendor/classList/classList.min.js: { weight: -21, browsers: { IE: 'lte IE 9', '!IE': false }, minified: true }
+  deprecated: The "%library_id%" asset library is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Use the the native browser implementation instead. See https://www.drupal.org/node/3089511
 
 ckeditor:
   remote: https://github.com/ckeditor/ckeditor-dev

core/tests/Drupal/Tests/Listeners/DeprecationListenerTrait.php

@@ -192,6 +192,7 @@ public static function getSkippedDeprecations() {
       'Drupal\Tests\BrowserTestBase::$defaultTheme is required in drupal:9.0.0 when using an install profile that does not set a default theme. See https://www.drupal.org/node/2352949, which includes recommendations on which theme to use.',
       'The "core/matchmedia" asset library is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. See https://www.drupal.org/node/3086653',
       'The "core/matchmedia.addListener" asset library is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. See https://www.drupal.org/node/3086653',
+      'The "core/classList" asset library is deprecated in drupal:8.8.0 and is removed from drupal:9.0.0. Use the the native browser implementation instead. See https://www.drupal.org/node/3089511',
     ];
   }