feat(12.2-04): edit related records in modals and defer relation work on new records

- RelationManager renders create/link/delete/unlink in declared order with
  one primary, opens the child modal (update or view form) or the pivot
  modal on row click, and deletes selected children behind a busy confirm
- RelationChildModal creates and edits children with its own session key
  (X-Child-Session-Key) so uploads and dates work inside it
- RelationPivotModal edits link details; the picker links one record with
  its pivot values when the relation has a pivot form
- deferrable managers render on the create screen with owner id 0, the
  form's X-Session-Key and the pending note, and mark the form dirty
- the registry resolves RelationManager lazily (child forms close an
  import cycle); DataTable gains openable rows and a trailing cell
- relation lang keys in en and pl; rebuilt boardwalk dist

admin/tests/fixtures/deferred.form-schema.json

@@ -38,6 +38,13 @@
           "mode": "crop"
         },
         "useCaption": true
+      },
+      {
+        "name": "parts",
+        "label": "Parts",
+        "type": "relation-manager",
+        "relation": "parts",
+        "deferrable": true
       }
     ],
     "messages": {