Merge branch 'node-children-compatibility' into 'release/0.9.0'

fix: NodeChildren伪装为Array保证向前兼容

保证VU调用 ({}).toString.call(children) === '[object Array]'

See merge request !867878

packages/designer/src/document/node/node-children.ts

@@ -285,4 +285,9 @@ export class NodeChildren {
     this.purged = true;
     this.children.forEach(child => child.purge());
   }
+
+  get [Symbol.toStringTag]() {
+    // 保证向前兼容性
+    return "Array";
+  }
 }