Issue #2350503 by dawehner: Add route generation handlers for entities

core/core.services.yml

core/lib/Drupal/Core/Entity/EntityManager.php

core/lib/Drupal/Core/Entity/EntityManagerInterface.php

core/lib/Drupal/Core/Entity/EntityType.php

core/lib/Drupal/Core/Entity/EntityTypeInterface.php

...upal/Core/Entity/Routing/EntityRouteProviderInterface.php

...al/Core/EventSubscriber/EntityRouteProviderSubscriber.php

core/modules/node/node.routing.yml

core/modules/node/src/Entity/Node.php

core/modules/node/src/Entity/NodeRouteProvider.php

core/modules/user/src/Entity/User.php

core/modules/user/src/Entity/UserRouteProvider.php

core/modules/user/user.routing.yml

core/tests/Drupal/Tests/Core/Entity/EntityManagerTest.php