Move constants to shared

Apparently we can't depend on react/src/ because the whole package is
considered "external" as far as rollup is concerned.

packages/react-dom/src/server/ReactPartialRenderer.js

@@ -18,7 +18,7 @@ import getComponentName from 'shared/getComponentName';
 import describeComponentFrame from 'shared/describeComponentFrame';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
 import {initializeLazyComponentType} from 'shared/ReactLazyComponent';
-import {Resolved, Rejected, Pending} from 'react/src/ReactLazy';
+import {Resolved, Rejected, Pending} from 'shared/ReactLazyStatusTags';
 import {
   warnAboutDeprecatedLifecycles,
   disableLegacyContext,

packages/react-reconciler/src/ReactFiberLazyComponent.js

@@ -9,7 +9,7 @@
 
 import type {LazyComponent} from 'react/src/ReactLazy';
 
-import {Resolved} from 'react/src/ReactLazy';
+import {Resolved} from 'shared/ReactLazyStatusTags';
 import {initializeLazyComponentType} from 'shared/ReactLazyComponent';
 
 export function resolveDefaultProps(Component: any, baseProps: Object): Object {

packages/react/src/ReactLazy.js

@@ -43,18 +43,13 @@ export type LazyComponent<T> =
   | ResolvedLazyComponent<T>
   | RejectedLazyComponent;
 
-export const Uninitialized = -1;
-export const Pending = 0;
-export const Resolved = 1;
-export const Rejected = 2;
-
 export function lazy<T>(
   ctor: () => Thenable<{default: T, ...} | T, mixed>,
 ): LazyComponent<T> {
   let lazyType: LazyComponent<T> = {
     $$typeof: REACT_LAZY_TYPE,
     // React uses these fields to store the result.
-    _status: Uninitialized,
+    _status: -1,
     _result: ctor,
   };
 

packages/shared/ReactLazyComponent.js

@@ -14,7 +14,12 @@ import type {
   LazyComponent,
 } from 'react/src/ReactLazy';
 
-import {Uninitialized, Pending, Resolved, Rejected} from 'react/src/ReactLazy';
+import {
+  Uninitialized,
+  Pending,
+  Resolved,
+  Rejected,
+} from './ReactLazyStatusTags';
 
 export function refineResolvedLazyComponent<T>(
   lazyComponent: LazyComponent<T>,

packages/shared/ReactLazyStatusTags.js

@@ -0,0 +1,14 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+// TODO: Move this to "react" once we can import from externals.
+export const Uninitialized = -1;
+export const Pending = 0;
+export const Resolved = 1;
+export const Rejected = 2;