fix: Make calls of the refetch() & fetchMore() trigger loading state

[nevermin9]

Description

This PR makes call of the refetch() or fetchMore() trigger loading.value to change.

Motivation

First, this issue.
Second, in the previous version of vue-apollo, $apollo.queries["query-name"].loading was changed every time when we call fetchMore()/refetch() or just changed values of the variables. And such behavior was very handy, reliable and expectable.
Now, call of the refetch() sets true into loading.value, but doesn't set false when refetching is complete. fatchMore() doesn't change value of loading.value at all.
Enabling notifyOnNetworkStatusChange option is not a good idea, bc on the same page we can have several components and if both of them enable such notifyOnNetworkStatusChange, both will show their loading states while only one component was calling refetch()/fetchMore() etc.
Loading state in one component has to stay independent from loading states of other components.

Testing notes

All tests are passed.
I checked @vue/apollo-composable with this fix in my project and everything works as expected.