docs-bug(treeview): Add guide on how to migrate from old treeview to new treeview

Documentation Feedback

Following the sudden deprecation of the various tree controllers, it would be nice if there were some kind of documentation on how to remove tree controller and migrate to the new way of doing things. Also, the documentation still contains references to treeControl, which it shouldn't because the treeControl has been deprecated?

A simple migration guide would be warranted as well because there are tonnes of search results and guides on how to use the tree that just became out of date, so if there was an easy way to adapt code to the new way of doing things, that would be ideal.

Affected documentation page

https://material.angular.io/components/tree/overview

从 https://material.angular.io/components/tree/overview 的 tree 概览页面开始，检查其中当前对 treeControl 的引用和指导。记录从已弃用的 tree 控制器迁移到新的 tree 方法的过程，并删除或更新过时的引用，以便页面提供清晰的迁移路径。