[improvement] Actionsheet: add cancel event (#796)

docs/demos/views/actionsheet.vue

@@ -7,7 +7,7 @@
 
     <demo-block :title="$t('title2')">
       <van-button @click="show2 = true">{{ $t('button2') }}</van-button>
-      <van-actionsheet v-model="show2" :actions="actions" :cancel-text="$t('cancel')" />
+      <van-actionsheet v-model="show2" :actions="actions" :cancel-text="$t('cancel')" @cancel="handleCancel" />
     </demo-block>
 
     <demo-block :title="$t('title3')">
@@ -61,6 +61,10 @@ export default {
   methods: {
     onClick(item) {
       Toast(item.name);
+    },
+    
+    handleCancel() {
+      Toast('cancel');
     }
   }
 };

docs/markdown/en-US/actionsheet.md

@@ -72,6 +72,12 @@ Actionsheet will get another style if there is a `title` prop.
 | close-on-click-overlay | Whether to close when click overlay | `Boolean` | - | - |
 | get-container | Return the mount node for actionsheet | `Function` | - | `() => HTMLElement` |
 
+### Event
+
+| Event | Description | Arguments |
+|-----------|-----------|-----------|
+| cancel | Triggered when cancel click | - |
+
 ### Data struct of actions
 
 | key | Description |

docs/markdown/zh-CN/actionsheet.md

@@ -75,6 +75,12 @@ export default {
 | close-on-click-overlay | 点击遮罩是否关闭`Actionsheet` | `Boolean` | - | - |
 | get-container | 指定挂载的 HTML 节点 | `Function` | - | `() => HTMLElement` |
 
+### Event
+
+| 事件名 | 说明 | 参数 |
+|-----------|-----------|-----------|
+| cancel | 取消按钮点击时触发 | - |
+
 ### actions
 
 `API`中的`actions`为一个对象数组，数组中的每一个对象配置每一列，每一列有以下`key`：