feat(DropdownItem): add lazy-render prop (#6454)

src/dropdown-menu/README.md

@@ -128,6 +128,7 @@ Use `active-color` prop to custom active color of the title and options
 | title | Item title | _string_ | Text of selected option |
 | options | Options | _Option[]_ | `[]` |
 | disabled | Whether to disable dropdown item | _boolean_ | `false` |
+| lazy-render `v2.8.5` | Whether to lazy render util opened | _boolean_ | `true` |
 | title-class | Title class | _string_ | - |
 | get-container `v2.2.4` | Return the mount node for menu | _string \| () => Element_ | - |
 

src/dropdown-menu/README.zh-CN.md

@@ -132,6 +132,7 @@ export default {
 | title | 菜单项标题 | _string_ | 当前选中项文字 |
 | options | 选项数组 | _Option[]_ | `[]` |
 | disabled | 是否禁用菜单 | _boolean_ | `false` |
+| lazy-render `v2.8.5` | 是否在首次展开时才渲染菜单内容 | _boolean_ | `true` |
 | title-class | 标题额外类名 | _string_ | - |
 | get-container `v2.2.4` | 指定挂载的节点，[用法示例](#/zh-CN/popup#zhi-ding-gua-zai-wei-zhi) | _string \| () => Element_ | - |