docs: add options-api for Transitions with the Key example

src/guide/built-ins/transition.md

@@ -587,6 +587,8 @@ Sometimes you need to force the re-render of a DOM element in order for a transi
 
 Take this counter component for example.
 
+<div class="composition-api">
+
 ```vue
 <script setup>
 import { ref } from 'vue';
@@ -602,10 +604,51 @@ setInterval(() => count.value++, 1000);
 </template>
 ```
 
+</div>
+<div class="options-api">
+
+```vue
+<script>
+export default {
+  data() {
+    return {
+      count: 1,
+      interval: null 
+    }
+  },
+  mounted() {
+    this.interval = setInterval(() => {
+      this.count++;
+    }, 1000)
+  },
+  beforeDestroy() {
+    clearInterval(this.interval)
+  }
+}
+</script>
+
+<template>
+  <Transition>
+    <span :key="count">{{ count }}</span>
+  </Transition>
+</template>
+```
+
+</div>
+
 If we had excluded the `key` attribute, only the text node would be updated and thus no transition would occur. However, with the `key` attribute in place, Vue knows to create a new `span` element whenever `count` changes and thus the `Transition` component has 2 different elements to transition between.
 
+<div class="composition-api">
+
 [Try it in the Playground](https://play.vuejs.org/#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)
 
+</div>
+<div class="options-api">
+
+[Try it in the Playground](https://play.vuejs.org/#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)
+
+</div>
+
 ---
 
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