Live resolvers: return value when throw

[pavelglac]

Return value when resolvers throw

Based on the docs :

If an individual resolver throws an error, when that field is read, Relay will log that error to the environment's user-provided relayFieldLogger logger, and the field will become null.

I am assuming the return value for resolvers should be null instead of the current undefined. However, tests for react-relay mark undefined as the expected value.

The fix would be to also save the return value from evaluation in LiveResolverCache.js
and not only the snapshot and error.

PR with suggested changes: #4876

[alloy]

Perhaps good to note that this result changed between Relay v17 and v18.