Setup Wave 2 of Feature Flags for React Native (#28990)

## Summary

Sets up dynamic feature flags for `disableStringRefs`, `enableFastJSX`,
and `enableRefAsProp` in React Native (at Meta).

## How did you test this change?

```
$ yarn test
$ yarn flow fabric
```

Author: yungsters

packages/shared/forks/ReactFeatureFlags.native-fb-dynamic.js

@@ -19,10 +19,13 @@
 
 export const alwaysThrottleRetries = __VARIANT__;
 export const consoleManagedByDevToolsDuringStrictMode = __VARIANT__;
-export const enableEarlyReturnForPropDiffing = __VARIANT__;
+export const disableDefaultPropsExceptForClasses = __VARIANT__;
+export const disableStringRefs = __VARIANT__;
+export const enableAddPropertiesFastPath = __VARIANT__;
 export const enableDeferRootSchedulingToMicrotask = __VARIANT__;
+export const enableEarlyReturnForPropDiffing = __VARIANT__;
+export const enableFastJSX = __VARIANT__;
 export const enableInfiniteRenderLoopDetection = __VARIANT__;
+export const enableRefAsProp = __VARIANT__;
 export const enableUnifiedSyncLane = __VARIANT__;
 export const passChildrenWhenCloningPersistedNodes = __VARIANT__;
-export const disableDefaultPropsExceptForClasses = __VARIANT__;
-export const enableAddPropertiesFastPath = __VARIANT__;

packages/shared/forks/ReactFeatureFlags.native-fb.js

@@ -21,13 +21,16 @@ const dynamicFlags: DynamicExportsType = (dynamicFlagsUntyped: any);
 export const {
   alwaysThrottleRetries,
   consoleManagedByDevToolsDuringStrictMode,
-  enableEarlyReturnForPropDiffing,
+  disableDefaultPropsExceptForClasses,
+  disableStringRefs,
+  enableAddPropertiesFastPath,
   enableDeferRootSchedulingToMicrotask,
+  enableEarlyReturnForPropDiffing,
+  enableFastJSX,
   enableInfiniteRenderLoopDetection,
+  enableRefAsProp,
   enableUnifiedSyncLane,
   passChildrenWhenCloningPersistedNodes,
-  disableDefaultPropsExceptForClasses,
-  enableAddPropertiesFastPath,
 } = dynamicFlags;
 
 // The rest of the flags are static for better dead code elimination.
@@ -94,12 +97,6 @@ export const disableClientCache = true;
 export const enableServerComponentKeys = true;
 export const enableServerComponentLogs = true;
 
-// TODO: Roll out with GK. Don't keep as dynamic flag for too long, though,
-// because JSX is an extremely hot path.
-export const enableRefAsProp = false;
-export const disableStringRefs = false;
-export const enableFastJSX = false;
-
 export const enableReactTestRendererWarning = false;
 export const disableLegacyMode = false;
 export const disableDOMTestUtils = false;

packages/shared/forks/ReactFeatureFlags.test-renderer.native-fb.js

@@ -80,9 +80,9 @@ export const disableClientCache = true;
 export const enableServerComponentKeys = true;
 export const enableServerComponentLogs = true;
 
-export const enableRefAsProp = false;
-export const disableStringRefs = false;
-export const enableFastJSX = false;
+export const enableRefAsProp = true;
+export const disableStringRefs = true;
+export const enableFastJSX = true;
 
 export const enableReactTestRendererWarning = false;
 export const disableLegacyMode = false;