dillon1000/react

Preserve memoization guarantees for useCallback

Improves `@enablePreserveExistingMemoizationGuarantees` for the useCallback 
case. Similar to useMemo, we add an explicit `Memoize` instruction for the 
callback function itself _and_ for its dependencies. This means we'll assume the 
callback doesn't mutate any captured variables. 

TODO: check this with cases involving refs (should be allowed, but also not 
accidentally freeze the ref) and reassignment of locals (should be disallowed, 
though that might just be a validation we're missing today)