Issue #2232275 by alexpott: System menu blocks need to be able to depend on their menu entities.

core/lib/Drupal/Core/Config/Entity/ConfigEntityBase.php

...m/lib/Drupal/system/Plugin/Derivative/SystemMenuBlock.php

...tem/lib/Drupal/system/Tests/Block/SystemMenuBlockTest.php

core/profiles/minimal/config/block.block.stark_admin.yml

core/profiles/minimal/config/block.block.stark_tools.yml

core/profiles/standard/config/block.block.bartik_footer.yml

core/profiles/standard/config/block.block.bartik_tools.yml

...pal/Tests/Core/Config/Entity/ConfigEntityBaseUnitTest.php