Issue #3086375 by zrpnr, lauriii, nod_: Deprecate domready and remove usages in core

core/core.libraries.yml

core/lib/Drupal/Core/Render/theme.api.php

core/misc/drupal.init.es6.js

core/misc/drupal.init.js

...ests/Drupal/KernelTests/Core/Asset/AttachedAssetsTest.php