feat(collapse-item): add size prop (#4829)

* feat(collapse-item): add size prop default null

* add docs

* fix docs

* Update README.md

* Update README.md

* Update index.ts

Co-authored-by: neverland <chenjiahan.jait@bytedance.com>

packages/collapse-item/index.ts

@@ -8,6 +8,7 @@ VantComponent({
   relation: useParent('collapse'),
 
   props: {
+    size: String,
     name: null,
     title: null,
     value: null,

packages/collapse-item/index.wxml

@@ -2,6 +2,7 @@
 
 <view class="van-collapse-item custom-class {{ index !== 0 ? 'van-hairline--top' : '' }}">
   <van-cell
+    size="{{ size }}"
     title="{{ title }}"
     title-class="title-class"
     icon="{{ icon }}"

packages/collapse/README.md

@@ -172,6 +172,7 @@ Page({
 | --- | --- | --- | --- |
 | name | 唯一标识符，默认为索引值 | _string \| number_ | `index` |
 | title | 标题栏左侧内容 | _string \| number_ | - |
+| size | 标题栏大小，可选值为`large` | _string_ | - |
 | icon | 标题栏左侧图标名称或图片链接，可选值见 [Icon 组件](#/icon) | _string_ | - |
 | value | 标题栏右侧内容 | _string \| number_ | - |
 | label | 标题栏描述信息 | _string_ | - |