feat(useVModel): add option to define defaultValue

[sondh0127]

Description

Add new option defaultValue to use when props value is not passed or undefined.
It can be useful in some situations:

My case: I'm using the same component(Modal) for CREATE and UPDATE a data model. I need to check if props passed or not to make sync of existing data (from API), this is for UPDATE. And for CREATE: I need some default data to let my form work property with v-model

const type = useVModel(props, 'type', emit)
const _type = ref('')
if (type.value)
  syncRef(type, _type) // old syncRef

simply

const type = useVModel(props, 'type', emit, { defaultValue: 'none' )

Additional context

This is similar to Uncontrolled | Controlled component from
https://ahooks.js.org/hooks/use-controllable-value

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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