✨ [Feature]: grid 树型表格组件添加getTreeExpandRecords获取已展开的节点方法

[David-TechNomad]

What problem does this feature solve

grid 树型表格组件添加getTreeExpandRecords获取已展开的节点方法，页面可以展示目前展开的数据

What does the proposed API look like

getTreeExpandRecords()，返回Array

What is your project name

bom树表组件

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Title: ✨ [Feature]: grid tree table component adds getTreeExpandRecords method to obtain expanded nodes

[gimmyhehe]

@David-TechNomad 经过评估该新特性有较强的实用性，需待安排开发~ 如果你对此新特性感兴趣，也欢迎提交PR~

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@David-TechNomad After evaluation, this new feature has strong practicality and needs to be developed~ If you are interested in this new feature, you are also welcome to submit a PR~