types(withDefaults): improve the type of boolean attribute value

[zqran]

Before:

const props = withDefaults(defineProps<{ active?: boolean }>(), {
  active: undefined
})
props.active // boolean
props.active.toString() // error!

After:

const props = withDefaults(defineProps<{ active?: boolean }>(), {})
props.active // boolean

const props = withDefaults(defineProps<{ active?: boolean }>(), {
  active: undefined
})
props.active // boolean | undefined

Also matches the following usages:

export default defineComponent({
  props: {
    active: {
      type: Boolean,
      required: false,
      default: undefined
    }
  },

  setup(props) {
    props.active // boolean | undefined
  }
})

---

Related to: #8576

[rxliuli]

Where is it blocked now? Why not merge it?

[zqran]

Where is it blocked now? Why not merge it?

There are no members to review this PR yet, maybe you can @ some members to take a look.