feat： 增加input 不设置placeholder的placeholder-style测试例

pages/component/input/input.uvue

@@ -51,7 +51,11 @@
         <view class="input-wrapper">
           <input id="uni-input-placeholder2" class="uni-input" :placeholder-class="inputPlaceHolderClass"
             placeholder="占位符字体大小为10px" />
-        </view>
+        </view>
+        <view class="input-wrapper">
+          <input class="uni-input" :placeholder-style="inputPlaceHolderStyle"
+            value="不设置placeholder只设置placeholder-style" />
+        </view>
       </view>
 
       <view>