More memoization in useFragmentInternal

Summary:
Adds some extra memoization in useFragmentInternal() to reduce work in the common case. Specifically, by memoizing the selector we ensure that the `areEqualSelectors()` call can hit the fast path, quickly bailing out when the inputs are `===`.

This also avoids unnecessarily running effects related to missing client edges (a further optimization would be to use static knowledge of the fragment to avoid running effects *at all* if we know the fragment can never have client edges).

Reviewed By: voideanvalue

Differential Revision: D36649352

fbshipit-source-id: 8ae7801a3d2644b2de162985dc650739731e18aa

packages/react-relay/relay-hooks/react-cache/useFragmentInternal_REACT_CACHE.js

@@ -273,7 +273,10 @@ function useFragmentInternal_REACT_CACHE(
   queryOptions?: FragmentQueryOptions,
   fragmentKey?: string,
 ): ?SelectorData | Array<?SelectorData> {
-  const fragmentSelector = getSelector(fragmentNode, fragmentRef);
+  const fragmentSelector = useMemo(
+    () => getSelector(fragmentNode, fragmentRef),
+    [fragmentNode, fragmentRef],
+  );
 
   const isPlural = fragmentNode?.metadata?.plural === true;