Override renderFunction for getDataFromTree when using React Native.

React Native is obviously not Node.js, but it also doesn't identify itself
as a browser-like environment, so importing `react-dom/server` fails due
to the transitive dependency on Node's built-in `stream` module:
#2592 (comment)

To fix this problem, we need to avoid automatically importing
`react-dom/server` in React Native (especially since `getDataFromTree` is
unlikely to be used in RN apps). Since module dependencies are effectively
static, detecting React Native at runtime is not an option, so we need
help from the React Native bundler. Specifically, if we import the render
function from `react-dom/server` in a small wrapper module, we should be
able to override that module in React Native.

According to the documentation of "Platform-specific extensions," it
appears we can make this work using the `.native.js` file extension.
Specifically, React Native is supposed to prefer `lib/*.native.js` modules
to their `lib/*.js` counterparts:
https://facebook.github.io/react-native/docs/platform-specific-code#platform-specific-extensions

The `src/defaultRenderFunction.native.ts` module exports a default
function that throws an exception, which makes `getDataFromTree` fail with
a helpful error message in React Native. Calling `getMarkupFromTree` with
a custom `renderFunction` may be a little more work for React Native apps,
but that seems acceptable because server-side rendering is not a common
use case in React Native, compared to client/server web applications.

src/defaultRenderFunction.native.ts

@@ -0,0 +1,3 @@
+export default function(_: React.ReactNode): string {
+  throw new Error("Please use getMarkupFromTree with a custom renderFunction in React Native");
+}

src/defaultRenderFunction.ts

@@ -0,0 +1,3 @@
+export {
+  renderToStaticMarkup as default
+} from "react-dom/server";

src/getDataFromTree.ts

@@ -1,6 +1,6 @@
 import * as React from 'react';
 import * as PropTypes from 'prop-types';
-import { renderToStaticMarkup } from 'react-dom/server';
+import defaultRenderFunction from './defaultRenderFunction';
 import Query from './Query';
 
 // Like a Set, but for tuples. In practice, this class is used to store
@@ -93,14 +93,14 @@ export default function getDataFromTree(
     context,
     // If you need to configure this renderFunction, call getMarkupFromTree
     // directly instead of getDataFromTree.
-    renderFunction: renderToStaticMarkup,
+    renderFunction: defaultRenderFunction,
   });
 }
 
 export type GetMarkupFromTreeOptions = {
   tree: React.ReactNode;
   context?: { [key: string]: any };
-  renderFunction?: typeof renderToStaticMarkup;
+  renderFunction?: typeof defaultRenderFunction;
 };
 
 export function getMarkupFromTree({
@@ -109,7 +109,7 @@ export function getMarkupFromTree({
   // The rendering function is configurable! We use renderToStaticMarkup as
   // the default, because it's a little less expensive than renderToString,
   // and legacy usage of getDataFromTree ignores the return value anyway.
-  renderFunction = renderToStaticMarkup,
+  renderFunction = defaultRenderFunction,
 }: GetMarkupFromTreeOptions): Promise<string> {
   const renderPromises = new RenderPromises();