Log MissingFieldErrors in ObservableQuery#getCurrentResult rather than using result.error

[benjamn]

Should fix #8593, which suggests our decision in #8262 to include MissingFieldErrors in result.error (beginning in @apollo/client@3.4.0-rc.1) was probably more disruptive than helpful.

[hueter]

This would help my team's issues a lot, thank you for the quick turnaround!

[tvler]

is there a way to suppress this manually for the time being until this is shipped?

[brainkim]

Two non-blocking questions:

1. How does this affect users who are now expecting one of data, error, loading to be defined? (Query data and error are undefined #8063)
2. What is the root cause of these transitory missing field errors, regardless of whether or not they’re logged or added to the result?

[benjamn]

@brainkim

1. We should keep looking for ways to prevent or explain situations where data, error, and/or loading have nonsensical/inconsistent values, but providing missing field errors via result.error (which I know I supported for in pass along missing field errors to the user #8262) was not the answer. This PR contributes to the explainability story by making it possible to recover the hidden errors by calling setLogVerbosity("debug"), but I don't expect this to be our last attempt to solve this problem.

2. Missing field errors are natural and expected in the course of using InMemoryCache. The cache doesn't start out with anything in it, yet we read from the empty cache in many normal situations, and that produces missing field errors. The errors become problematic when you're reading data that you expected to exist, which can happen due to cache eviction (for example) or lists populated by different queries with incompatible selection sets. Unfortunately, I don't know how to tell the difference between what was expected versus what was surprising, so I think we need to prioritize not erroring when nothing's actually wrong, so people can update from v3.3.x to v3.4.x without worrying about this new source of errors.

[brainkim]

LGTM