feat(Button): add loading-type prop (#1955)

example/pages/button/index.wxml

@@ -26,6 +26,7 @@
 
   <demo-block title="加载状态" padding>
     <van-button loading type="primary" class="demo-margin-right" />
+    <van-button loading type="primary" loading-type="spinner" class="demo-margin-right" />
     <van-button loading type="danger" loading-text="加载中..." />
   </demo-block>
 

packages/button/README.md

@@ -56,6 +56,7 @@
 
 ```html
 <van-button loading type="primary" />
+<van-button loading type="primary" loading-type="spinner" />
 <van-button loading type="danger" loading-text="加载中..." />
 ```
 
@@ -63,7 +64,7 @@
 
 通过`icon`属性设置按钮图标，支持 Icon 组件里的所有图标，也可以传入图标 URL
 
-```html 
+```html
 <van-button icon="star-o" type="primary" />
 <van-button icon="star-o" type="primary">按钮</van-button>
 <van-button icon="https://img.yzcdn.cn/vant/logo.png" type="danger">按钮</van-button>
@@ -113,6 +114,7 @@
 | hairline | 是否使用 0.5px 边框 | *boolean* | `false` |
 | loading | 是否显示为加载状态 | *boolean* | `false` |
 | loading-text | 加载状态提示文字 | *string* | - |
+| loading-type | 加载状态图标类型，可选值为 `spinner` | *string* | `circular` |
 | loading-size | 加载图标大小 | *string* | `20px` |
 | open-type | 微信开放能力，具体支持可参考 [微信官方文档](https://mp.weixin.qq.com/debug/wxadoc/dev/component/button.html) | *string* | - |
 | app-parameter | 打开 APP 时，向 APP 传递的参数 | *string* | - |

packages/button/index.ts

@@ -21,6 +21,10 @@ VantComponent({
     hairline: Boolean,
     disabled: Boolean,
     loadingText: String,
+    loadingType: {
+      type: String,
+      value: 'circular'
+    },
     type: {
       type: String,
       value: 'default'

packages/button/index.wxml

@@ -27,6 +27,7 @@
     <van-loading
       custom-class="loading-class"
       size="{{ loadingSize }}"
+      type="{{ loadingType }}"
       color="{{ type === 'default' ? '#c9c9c9' : '' }}"
     />
     <view