Make client.{reset,clear}Store pass appropriate discardWatches option to cache.reset

[benjamn]

Follow-up to PR #8852, inspired by discussion #8872 started by @KeithGillette. Depending on the discussion, we may need to make additional changes to align the various store-resetting/clearing operations, so I've left this PR as a draft for now.

[benjamn]

The QueryManager#resetStore method is no longer needed, because ApolloClient#resetStore actually just calls client.queryManager.clearStore, and QueryManager is a private API.

[benjamn]

This helper function allows us to preserve existing tests that called qm.resetStore() (now removed).

[KeithGillette]

Thanks for responding so quickly to my discussion #8872, @benjamn. In looking at these changes, it appears to me that If this PR is merged, both ApolloClient.resetStore() and ApolloClient.clearStore() will call the QueryManager.reset() with different parameter values and that QueryManager.reset() in turn calls cache.reset(). If that's true, I think that answers my question regarding the relationship of the APIs, which was only prompted by the mention in the CHANGELOG of changes to cache.reset()` from PR #8852.

As a consumer of ApolloClient, I'm really only concerned about the public API, so my bigger question regarding the use cases for resetStore vs. clearStore is still unresolved. As I said in the discussion, the documented recommendation to use resetStore on user sign out and have that method refetch active queries never made sense to me, as it ends up reloading data into the cache and can lead to errors on active queries requiring authorization. If clearStore cancels any active queries then clears the cache, it would seem to me that would be the best method to use on user sign out, with resetStore preferred for use in quickly clearing all cache contents within a user session.

I may be way off base on all of that, but I guess my recommendation is that this PR include documentation updates that clearly differentiate the appropriate use cases for resetStore vs. clearStore.

[hwillson]

Looks great to me @benjamn - thanks!

[benjamn]

The initial code changes from this commit are now available in @apollo/client@3.4.16 and @apollo/client@3.5.0-rc.1.

While I agree the docs could take a stronger stance on which method (resetStore or clearStore) is recommended after logout, we do at least mention both methods and their differences here and here.

My intuition is that resetStore is a good way to switch into a cache/UI state that approximates what you'd see if the page was initially loaded without authentication, whereas clearStore is more for situations where you expect the user to close the page and leave soon. Yes, there may be authentication errors with resetStore refetching queries, but if you're handling those errors gracefully, resetStore can be an easy way to re-render the logged-out UI.