Fix ReactFiberReconciler annotation to include PI

#8628 (comment)

Author: iamdustan

src/renderers/shared/fiber/ReactFiberReconciler.js

@@ -170,7 +170,7 @@ module.exports = function<T, P, I, TI, PI, C, CX>(config : HostConfig<T, P, I, T
 
     deferredUpdates,
 
-    getPublicRootInstance(container : OpaqueNode) : (ReactComponent<any, any, any> | I | TI | null) {
+    getPublicRootInstance(container : OpaqueNode) : (ReactComponent<any, any, any> | I | TI | PI | null) {
       const root : FiberRoot = (container.stateNode : any);
       const containerFiber = root.current;
       if (!containerFiber.child) {

src/renderers/testing/ReactTestRendererFiber.js

@@ -189,7 +189,7 @@ var TestRenderer = ReactFiberReconciler({
 
   useSyncScheduling: true,
 
-  getPublicInstance(inst) {
+  getPublicInstance(inst : Instance | TextInstance) {
     switch (inst.tag) {
       case 'INSTANCE':
         const createNodeMock = inst.rootContainerInstance.createNodeMock;