feat(useVModel): add shouldEmit hook

[baiwusanyu-c]

Warning: ⚠️ Slowing down new functions

Due to the growing audience of VueUse, we received a huge amount of feature requests and pull requests. It's become harder and harder and recently a bit beyond our capacity to maintain the project. In the near future, we could like slowing down on accepting new features and prioritize the stability and quality of existing functions. New functions to VueUse may not be accpected. If you come up some new ideas, we advice you to have them in your codebase first instead of proposing to VueUse. You may iterate them a few time and see how them suite your needs and how them can be generalized. If you really believe they are useful to the community, you can create PR with your usercases, we are still happy to hear and discuss. Thank you for your understanding.

Description

I encountered a scenario that is in the complex form component A, usually we will use it as the parent component, and implement the v-model in the child component B, but when using useVModel, it automatically triggers the emit event, which makes I can only write the verification rules in component A. When the form is very complicated, it will become very bloated. I want to have a hook method, verify in the hook method, and decide whether to start based on the verification result emit event.

// A.vue
<template>
  <B  v-model='foo' />
</template>

// B.vue
<template>
   .....
</template>

<script setup>
  const props = definedProps(['modelValue'])
  const emits = definedEmits(['update:modelValue'])
  const data = useVModel(props,  'modelValue', emits, { beforeEmit })
  function beforeEmit(value) {
    // If the verification fails, return false and the emit event will not be triggered
    if(value === 1) return false 
    return true
 }
</script>

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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