Slider: fix #15545 by adding explains about "input" event in Chinese (#15588)

Slider: add explains about "input" event (#15545)

examples/docs/en-US/slider.md

@@ -237,4 +237,5 @@ Selecting a range of values is supported.
 | Event Name | Description | Parameters |
 |---------- |-------- |---------- |
 | change | triggers when the value changes (if the mouse is being dragged, this event only fires when the mouse is released) | value after changing |
+| input | triggers when the data changes (It'll be emitted in real time during sliding) | value after changing |
 

examples/docs/es/slider.md

@@ -239,4 +239,5 @@ Se soporta la selección de un rango de valores.
 | Nombre | Descripción                              | Parametros               |
 | ------ | ---------------------------------------- | ------------------------ |
 | change | se dispara cuando el valor cambia (si el ratón está comenzando el arrastre este evento sólo se disparara cuando se suelte el ratón) | valor despues del cambio |
+| input | triggers when the data changes (It'll be emitted in real time during sliding) | value after changing |
 

examples/docs/fr-FR/slider.md

@@ -237,3 +237,4 @@ Vous pouvez sélectionner des intervalles de valeurs au lieu d'une valeur unique
 | Nom | Description | Paramètres |
 |---------- |-------- |---------- |
 | change | Se déclenche quand la valeur change (si le changement est fait à la souris, se déclenche quand la souris redevient immobile). | La nouvelle valeur. |
+| input | triggers when the data changes (It'll be emitted in real time during sliding) | value after changing |

examples/docs/zh-CN/slider.md

@@ -234,3 +234,4 @@
 | 事件名称      | 说明    | 回调参数      |
 |---------- |-------- |---------- |
 | change | 值改变时触发（使用鼠标拖曳时，只在松开鼠标后触发） | 改变后的值 |
+| input | 数据改变时触发（使用鼠标拖曳时，活动过程实时触发） | 改变后的值 |

packages/slider/src/main.vue

@@ -13,7 +13,7 @@
       v-if="showInput && !range"
       class="el-slider__input"
       ref="input"
-      @change="$nextTick(emitChange)"
+      @change="emitChange"
       :step="step"
       :disabled="sliderDisabled"
       :controls="showInputControls"