[Fiber] Implement test renderer (#8628)

* ReactTestRenderer move current impl to stack dir

* ReactTestRenderer on fiber: commence!

* ReactTestRenderer: most non-ref/non-public-instance tests are passing

* Move ReactTestFiberComponent functions from Renderer to Component file

* test renderer: get rid of private root containers and root Maps

* TestRenderer: switch impl based on ReactDOMFeatureFlag.useFiber

* ReactTestRenderer: inline component creation

* ReactTestRenderer: return to pristine original glory (+ Fiber for error order difference)

* TestRendererFiber: use a simple class as TestComponentInstances

* Add `getPublicInstance` to support TestRenderer `createNodeMock`

* Rename files to end. Update for `mountContainer->createContainer` change

* test renderer return same object to prevent unnecessary context pushing/popping

* Fiber HostConfig add getPublicInstance. This should be the identity fn everywhere except the test renderer

* appease flow

* Initial cleanup from sleepy work

* unstable_batchedUpdates

* Stack test renderer: cache nodeMock to not call on unmount

* add public instance type parameter to the reconciler

* test renderer: set _nodeMock when mounted

* More cleanup

* Add test cases for root fragments and (maybe?) root text nodes

* Fix the npm package build

Explicitly require the Stack version by default.
Add a separate entry point for Fiber.

We don't add fiber.js to the package yet since it's considered internal until React 16.

* Relax the ref type from Object to mixed

This seems like the most straightforward way to support getPublicInstance for test renderer.

* Remove accidental newline

* test renderer: unify TestComponent and TestContainer, handle root updates

* Remove string/number serialization attempts since Fiber ensures all textInstances are strings

* Return full fragments in toJSON

* Test Renderer remove TestComponent instances for simple objects

* Update babylon for exact object type syntax

* Use $$typeof because clarity > punching ducks.

* Minor Flow annotation tweaks

* Tweak style, types, and naming

* Fix typo

Author: iamdustan

fiber.js

@@ -0,0 +1,3 @@
+'use strict';
+
+module.exports = require('./lib/ReactTestRendererFiber');

index.js

@@ -1,3 +1,3 @@
 'use strict';
 
-module.exports = require('./lib/ReactTestRenderer');
+module.exports = require('./lib/ReactTestRendererStack');