Warn when closing Work item with open children

...ts/javascripts/work_items/components/work_item_drawer.vue

...ascripts/work_items/components/work_item_state_toggle.vue

...scripts/work_items/graphql/open_child_count.query.graphql

...s/work_items/graphql/work_item_hierarchy.fragment.graphql

...pts/work_items/graphql/work_item_widgets.fragment.graphql

...pts/work_items/graphql/work_item_widgets.fragment.graphql

locale/gitlab.pot

...tend/work_items/components/work_item_state_toggle_spec.js

spec/frontend/work_items/mock_data.js

...rt/shared_examples/features/work_items_shared_examples.rb