4.x版本图例怎么配置默认置灰和高亮呢

- [ ] I have searched the [issues](https://github.com/antvis/f2/issues) of this repository and believe that this is not a duplicate.

### What problem does this feature solve?
比如5个图例，前2个默认置灰不选，后3个高亮，看3.x版本好像有checked。4.x就无了例外官网文档不全

### What does the proposed API look like?

类似a,b为高亮状态，不配为置灰

Start at the F2 v4 Legend entry point and compare its API with the referenced v3 `checked` behavior. Verify how `selected={[a,b]}` should represent highlighted and greyed items, then confirm the behavior in a legend example or existing legend tests; done means the requested default selection works and is documented.

Written by the indexing model from the issue text.