Fix suspense in useState and useReducer initializers

[kitten]

Fix FormidableLabs/next-urql#34

This fixes an edge case where a suspense is triggered in the useState initialiser (useState(() => throw Promise.resolve())) or in the useReducer's init argument (useReducer(x, y, () => throw Promise.resolve()))

This is achieved by ensuring that the hook's state is initialised before applying updates on a rerender, since the workInProgressHook will have already been created after suspense.

And subsequently we also fix the initialiser not being called on rerenders by instead checking whether the hook's state has been initialised.

Example: This may happen when useSubscription is used with a getCurrentValue function that may trigger suspense by throwing a promise, See: https://github.com/facebook/react/blob/4d9f8500651c5d1e19d8ec9a2359d5476a53814b/packages/use-subscription/src/useSubscription.js#L33-L37