子组件路由监听 无效

在mian下的子组件监听路由， deep：true，无效， immediate: true, 可以监听到 to参数，但是监听 from 参数 永远是 undefined， 不使用深度监听， 什么都没有

Start by reproducing the route watcher behavior in the main area’s child component, comparing deep and immediate watcher configurations. Trace how the route change callback receives its to and from values; done means the reported child-component case is reproducible, understood, and covered by a regression check showing the expected values.

Written by the indexing model from the issue text.