fix(graphcache): Re-enable offlineExchange issuing non-cache request policies

[kitten]

Summary

This PR, when applied, makes two changes.

Primarily, requesdt policies other than cache-first are now allowed in the offlineExchange when re-running failed operations. After rehydration or when replaying failed queries, queries will now not be forced to cache-first policies, and instead use the highest policy that was issued, preferring network policies (cache-only < cache-first < network-only < cache-and-network).

Additionally, instead of checking manually which mutations have made optimistic changes, the cacheExchange will now mark optimistic mutations' contexts with optimistic: true instead.

Set of changes

• Add OperationContext.optimistic indicating optimistic updates have been made
• Remove cache-first forcing in offlineExchange
• Pick highest policy that has been seen in offlineExchange
• Remove queries from failedQueue that have received a pre-hydration network result