[Improvement] Search: support native input attrs (#418)

docs/markdown/en-US/field.md

@@ -77,7 +77,7 @@ Textarea Filed can be auto resize when has `autosize` prop
 ```
 
 ### API
-Filed support all native properties of input tag，such as `maxlength`、`placeholder`、`readonly`
+Filed support all native properties of input tag，such as `maxlength`、`placeholder`、`readonly`、`autofocus`
 
 | Attribute | Description | Type | Default | Accepted Values |
 |-----------|-----------|-----------|-------------|-------------|

docs/markdown/en-US/search.md

@@ -55,6 +55,7 @@ Use `action` slot to custom right button, `cancel` event will no longer be trigg
 ```
 
 ### API
+Search support all native properties of input tag，such as `maxlength`、`placeholder`、`readonly`、`autofocus`
 
 | Attribute | Description | Type | Default | Accepted Values |
 |-----------|-----------|-----------|-------------|-------------|

docs/markdown/zh-CN/field.md

@@ -79,7 +79,7 @@ Vue.use(Field);
 ```
 
 ### API
-Filed 默认支持 Input 标签所有的原生属性，比如 `maxlength`、`placeholder`、`readonly` 等
+Filed 默认支持 Input 标签所有的原生属性，比如 `maxlength`、`placeholder`、`readonly`、`autofocus` 等
 
 | 参数 | 说明 | 类型 | 默认值 | 可选值 |
 |-----------|-----------|-----------|-------------|-------------|

docs/markdown/zh-CN/search.md

@@ -46,10 +46,10 @@ Tips: 在 `van-search` 外层增加 form 标签，并且 action 不为空，即
 ```
 
 ### API
+Search 默认支持 Input 标签所有的原生属性，比如 `maxlength`、`placeholder`、`readony`、`autofocus` 等
 
 | 参数 | 说明 | 类型 | 默认值 | 可选值 |
 |-----------|-----------|-----------|-------------|-------------|
-| placeholder | `input`的`placeholder`文案 | `String` | - | - |
 | background | 搜索框背景色 | `String` | `#f2f2f2` |  所有浏览器支持的颜色描述 |
 | showAction | 是否在搜索框右侧显示取消按钮 | `Boolean` | false | - |
 

packages/search/index.vue

@@ -8,14 +8,14 @@
       <input
         type="search"
         class="van-search__input"
+        v-bind="$attrs"
         v-refocus="focusStatus"
         :value="value"
-        :placeholder="placeholder"
         @input="onInput"
         @focus="onFocus"
         @keypress.enter.prevent="onSearch"
       >
-      <icon name="clear" @click="onClean" v-show="isFocus" />
+      <icon name="clear" v-show="isFocus && value" @click="onClean" />
     </div>
     <div class="van-search__action" v-if="showAction">
       <slot name="action">
@@ -35,7 +35,6 @@ export default create({
   props: {
     value: String,
     showAction: Boolean,
-    placeholder: String,
     background: {
       type: String,
       default: '#f2f2f2'