🤔 [QUESTION]请问一下有没有折线图区域高亮的功能

### 🐛 Question description [Please make everyone to understand it]

### 💻 Link to minimal reproduction

Please provide a link by forking these links [g2plot](https://codesandbox.io/s/g2plot-reproduction-template-gyej1) or GitHub repo. What is a minimal reproduction, and why is it required?

### 🏞 Expected result

### 🚑 Any additional [like screenshots]

* **G2Plot Version**:
* **Platform**:
这样的

Review G2Plot's line-chart documentation and current area-highlighting capabilities, using the attached image to clarify the intended result. The issue does not identify a reproduction, entry point, or acceptance criteria; done would require a confirmed scope and an agreed implementation path.

Written by the indexing model from the issue text.