[improvement] Tab: use transform to improve animation performance

docs/markdown/v2-progress-tracking.md

@@ -134,6 +134,7 @@
 
 ### Tab
 
+- 优化`animated`动画性能
 - 修复开启`animated`后高度错误的问题
 
 ### Tabbar

packages/tab/test/__snapshots__/demo.spec.js.snap

@@ -206,7 +206,7 @@ exports[`renders demo correctly 1`] = `
         </div>
       </div>
       <div class="van-tabs__content">
-        <div class="van-tabs__track" style="left: 0%; transition-duration: 0.3s;">
+        <div class="van-tabs__track" style="transform: translate3d(0%, 0, 0); transition-duration: 0.3s;">
           <div class="van-tab__pane-wrapper">
             <div class="van-tab__pane">
               内容 1

packages/tabs/index.js

@@ -111,7 +111,7 @@ export default sfc({
     trackStyle() {
       if (this.animated) {
         return {
-          left: `${-1 * this.curActive * 100}%`,
+          transform: `translate3d(${-1 * this.curActive * 100}%, 0, 0)`,
           transitionDuration: `${this.duration}s`
         };
       }