Add flow types RNTester examples (#22829)

Summary:
This PR adds flow types for the RNTester examples, and updates all of the RNTester examples to match the flow type consistently.

Previously, there was a mix of static class definitions and whether or not pages exported examples or a component. Now we will always export the same way, enforced by flow types

Note: I also fixed most of the $FlowFixMe in changed components
Pull Request resolved: facebook/react-native#22829

Reviewed By: cpojer

Differential Revision: D13563191

Pulled By: rickhanlonii

fbshipit-source-id: b697e3346a863d1b130881592b0522a96c202b63

Author: rickhanlonii

ViewPagerAndroidExample.android.js

@@ -33,7 +33,9 @@ const IMAGE_URIS = [
   'https://apod.nasa.gov/apod/image/1510/lunareclipse_27Sep_beletskycrop4.jpg',
 ];
 
-class LikeCount extends React.Component {
+type Props = $ReadOnly<{||}>;
+type State = {|likes: number|};
+class LikeCount extends React.Component<Props, State> {
   state = {
     likes: 7,
   };
@@ -92,10 +94,6 @@ class ProgressBar extends React.Component {
 }
 
 class ViewPagerAndroidExample extends React.Component {
-  static title = '<ViewPagerAndroid>';
-  static description =
-    'Container that allows to flip left and right between child views.';
-
   state = {
     page: 0,
     animationsAreEnabled: true,
@@ -291,4 +289,15 @@ const styles = StyleSheet.create({
   },
 });
 
-module.exports = ViewPagerAndroidExample;
+exports.title = '<ViewPagerAndroid>';
+exports.description =
+  'Container that allows to flip left and right between child views.';
+
+exports.examples = [
+  {
+    title: 'Basic pager',
+    render(): React.Element<typeof ViewPagerAndroidExample> {
+      return <ViewPagerAndroidExample />;
+    },
+  },
+];