feat(watch): deep watch allow setting condition for skipping object

[kimverchan]

RFC: vuejs/rfcs#712

If you want to skip the dependency collection of an object when deeply watch to an object, you cannot do so currently. Add the skip attribute to watchOptions to do this. Examples are as follows:

let dummy = 0
const source = reactive({
    num1: 1,
    nested: { _skip: true, num2: 0 },
})
watch(source, () => dummy++, {
    deep: true,
    skip(val) {
      return val._skip // return true to skip val
    }
})
source.nested.num2++ // do not run callback
expect(dummy).toBe(0)
source.num1++ // run callback
expect(dummy).toBe(1)
source.nested.num2++  // do not run callback
expect(dummy).toBe(1)

[edison1105]

Adding new features needs to be discussed through an RFC, similar to PR #9572.