v4: Fixes useMutation not taking a Ref

[bbugh]

Currently, useMutation is defined to not allow document or options to be a Ref. It works as expected, it just needs to be unwrapped in mutate. Here is example code that breaks in v4-alpha4, but works after this PR.

const randomName = ref('')

const options = ref({ variables: { id: 1, name: randomName } })

// ❌ v4-alpha4 causes a type error on `options`
// ✅ works correctly after the PR
const { mutate } = useMutation(RandomNameMutation, options)

// button @click="randomizeName"
function randomizeName () {
  randomName.value = Math.random().toString()
  mutate()
}

In this case, clicking the button correctly runs the mutation with a new random name value every time.

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This PR resolves one of several issues found while creating a graphql-code-generator plugin for vue-apollo hooks, which can be tracked here.