optimistic update on the query itself instead of reaching out to the queryClient

[sahilmob]

Currently, the only way to do optimistic updates is to use queryClient.setQueeyData with the query key, however, in some cases, I get access to the query itself in the same place that I want to do the optimistic update in.

Basically what I'm asking for is an update function returned when useQuery is called, and this function may take an updater function or simply a new value.

const {update, ...} = useQuery(...)

to use it:

update(old =>  ({
    ...old,
    items: [...old.items, text],
 }))

instead of

const queryClient = useQueryClient()
queryClient.setQueryData('todos', old => ({
    ...old,
     items: [...old.items, text],
  }))

[sahilmob]

#3636 should close this.