Drastically simplify useQuery default options processing

[benjamn]

When implementing the new useQuery(query, { defaultOptions }) functionality in #9563, I fell under the (thankfully mistaken) impression that I needed to handle all defaulting of WatchQueryOptions within the createWatchQueryOptions method of the InternalState class that useQuery uses internally.

This PR demonstrates we can avoid that computation entirely, and rely instead on existing defaulting mechanisms (in watchQuery) to do the same job. The trick is to use the defaultOptions from useQuery(query, { defaultOptions }) only when we first create the ObservableQuery (that is, only when we call client.watchQuery). That way, the defaultOptions are only relevant once, and do not continue to interfere with WatchQueryOptions (re)computation after that.

This simplification means we no longer need to consider the "latest" values of default options in createWatchQueryOptions, because we no longer consider default options at all in createWatchQueryOptions. More generally, at the point in time when we provide defaultOptions (once, when calling client.watchQuery), we have not yet created the ObservableQuery, so there are no other option values to worry about, latest or otherwise.

By contrast, my previous code went to unnecessary lengths to give precedence to this.observable.options whenever there was a default option of the same name. Unfortunately, that trick (or at least the way I implemented it) did not work for the fetchPolicy option in conjunction with skip, since skip: true sets this.observable.options.fetchPolicy = "standby", and we do not want to recycle that standby value (even though it is technically the "latest" value) when we switch back to skip: false. Instead, we want the original/initial fetchPolicy to be restored at that point. Fixing this problem fixes the reproduction in #9635.

Should fix the following issues:

• 3.6.0 Some queries never executing with a conditional skip and overridden fetchPolicy #9635

[benjamn]

This is the crux of the new strategy, allowing all the other simplifications.

[hwillson]

Awesome - thanks @benjamn!