bug(mat-tree): How to control a tree expansion state if treeControl is deprecated?

### Is this a regression?

- [ ] Yes, this behavior used to work in the previous version

### The previous version in which this bug was not present was

_No response_

### Description

mat-tree has [treeControl] (and many other related classes and parts) deprecated. How are we supposed to control the expansion state of the tree from our component if there is to no treeControl? Was this an oversight in documentation? even your own examples in the documentation use the deprecated features!

### Reproduction

N/A

### Expected Behavior

I expect deprecated features / componenets / classes to have a new replacement or documentation on HOW to use the new way of doing things that accounts for the deprecated feature.

### Actual Behavior

In this case (CdkTree):

```
/**
* The tree controller
*
* @deprecated Use one of `levelAccessor` or `childrenAccessor` instead. To be removed in a
* future version.
* @breaking-change 21.0.0
*/
treeControl?: TreeControl;
```
levelAccessor and childrenAccessor have nothing to do with expansion state. Please tell us what we are supposed to use in place of treeControl!

### Environment

- Angular: 18.2.2
- CDK/Material: 18.2.2
- Browser(s): N/A
- Operating System (e.g. Windows, macOS, Ubuntu): N/A

首先查看 issue 中展示的 CdkTree API，以及现有使用 treeControl 的 mat-tree 文档示例。确定应如何通过非弃用 API 控制展开状态，然后更新指南和示例，使替代方案明确，并使文档化的方法完整。

由索引模型根据 Issue 内容生成。