fix(reactivity): ensure multiple effectScope on() and off() calls maintains correct active scope

[edison1105]

The following code does not work correctly in the current vapor branch. When the button is clicked, the button text does not update.

<script setup>
import { ref } from 'vue'
const count = ref(0)
</script>

<template>
  <button id="btn" @click="count++">{{ count }}</button>
  <div v-if="count < 1">{{ count }}</div>
  <div v-else>{{ count * 2 }}</div>
</template>

The issue is because scope.on is called twice:

• inside simpleSetCurrentInstance > i.scope.on()
• if (scope) scope.on()
  

  core/packages/runtime-vapor/src/renderEffect.ts

  Lines 30 to 31 in c2e7312

  	simpleSetCurrentInstance(instance)
  	if (scope) scope.on()

if scope equals i.scope the following happens

scope1.on()  // activeEffectScope = scope1, prevScope = undefined
scope1.on()  // activeEffectScope = scope1, prevScope = scope1 (❌)
scope1.off() // activeEffectScope = scope1 (❌)
scope1.off() // activeEffectScope = undefined

The core also has a similar issue, see #12631. It is also caused by scope.on() being called multiple times. I have already created a PR #12632 to fix it. The changes in #12632 aim to avoid redundant updates to currentInstance, while this PR supports multiple calls to on. If this PR is merged, #12632 will no longer be needed.

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