Issue #2051889 by dawehner, pwolanin, tstoeckler: Add route parameters property to menu links.

...odules/menu_link/lib/Drupal/menu_link/Entity/MenuLink.php

...ules/menu_link/lib/Drupal/menu_link/MenuLinkInterface.php

...u_link/lib/Drupal/menu_link/MenuLinkStorageController.php

core/modules/menu_link/menu_link.install

...rupal/menu_link/Tests/Plugin/Core/Entity/MenuLinkTest.php

...modules/system/lib/Drupal/system/Tests/Menu/LinksTest.php

core/modules/system/system.install