fix(graphcache): Fix partial optimistic mutation results

[kitten]

Resolve #2701

(NOTE: This is a missing piece that's also required to fix a new optimistic mutation case)

Summary

This adds a missing piece of logic that we forgot to update in #2616, which allows optimistic mutations to not only be based on the field name (not alias) and nested functions, but also to return partial results.

Previously to this fix, partial mutation updates would cause cache misses by deleting cache values instead of skipping them.

Set of changes

• Skip undefined fields on optimistic mutation results

[changeset-bot]

🦋 Changeset detected

Latest commit: f63c2be

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@urql/exchange-graphcache	Patch

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