Update docs and example to use BackButton (remix-run#5513)

Author: coreh

packages/react-router-native/docs/api/AndroidBackButton.md

@@ -0,0 +1,27 @@
+# <BackButton>
+
+Connects the global back button on Android and tvOS to the router's history. On Android, when the initial location is reached, the default back behavior takes over. Just render one somewhere in your app.
+
+```js
+<BackButton/>
+```
+
+## children
+
+If you want to avoid the floating configuration component, you can compose with children.
+
+```js
+<NativeRouter>
+  <BackButton>
+    <App/>
+  </BackButton>
+</NativeRouter>
+
+// instead of
+<NativeRouter>
+  <View>
+    <BackButton/>
+    <View>Some people don't like that.</View>
+  </View>
+</NativeRouter>
+```

packages/react-router-native/docs/api/BackButton.md

@@ -1,14 +1,14 @@
 import React from 'react'
 import { AppRegistry, StyleSheet, Text, View } from 'react-native'
 
-import { NativeRouter, Route, Link, DeepLinking, AndroidBackButton, Prompt } from './main'
+import { NativeRouter, Route, Link, DeepLinking, BackButton, Prompt } from './main'
 
 export default class ReactRouterNative extends React.Component {
   render() {
     return (
       <NativeRouter>
         <View style={styles.container}>
-          <AndroidBackButton/>
+          <BackButton/>
           <DeepLinking/>
 
           <Route exact path="/" render={() => (

packages/react-router-native/index.android.js

@@ -1,6 +1,6 @@
 export default {
   api: [
-    require('../../../react-router-native/docs/api/AndroidBackButton.md'),
+    require('../../../react-router-native/docs/api/BackButton.md'),
     require('../../../react-router-native/docs/api/DeepLinking.md'),
     require('../../../react-router-native/docs/api/Link.md'),
     require('../../../react-router-native/docs/api/NativeRouter.md'),

packages/react-router-website/modules/docs/Native.js

@@ -46,7 +46,7 @@ All of the package modules can be imported from the top:
 import {
   NativeRouter as Router,
   DeepLinking,
-  AndroidBackButton,
+  BackButton,
   Link,
   Route
   // etc.