[Flight] Chunks API (#17398)

* Add feature flags

* Add Chunk type and constructor

* Wire up Chunk support in the reconciler

* Update reconciler to reconcile Chunks against the render method

This allows the query and args to be updated.

* Drop the ref. Chunks cannot have refs anyway.

* Add Chunk checks in more missing cases

* Rename secondArg

* Add test and fix lazy chunks

Not really a supported use case but for consistency I guess.

* Fix fragment test

Author: sebmarkbage

src/ReactTestRenderer.js

@@ -36,6 +36,7 @@ import {
   Profiler,
   MemoComponent,
   SimpleMemoComponent,
+  Chunk,
   IncompleteClassComponent,
   ScopeComponent,
 } from 'shared/ReactWorkTags';
@@ -185,6 +186,14 @@ function toTree(node: ?Fiber) {
         instance: null,
         rendered: childrenToTree(node.child),
       };
+    case Chunk:
+      return {
+        nodeType: 'chunk',
+        type: node.type,
+        props: {...node.memoizedProps},
+        instance: null,
+        rendered: childrenToTree(node.child),
+      };
     case HostComponent: {
       return {
         nodeType: 'host',
@@ -222,6 +231,7 @@ const validWrapperTypes = new Set([
   ForwardRef,
   MemoComponent,
   SimpleMemoComponent,
+  Chunk,
   // Normally skipped, but used when there's more than one root child.
   HostRoot,
 ]);