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: https://github.com/facebook/react-native/pull/22829

Reviewed By: cpojer

Differential Revision: D13563191

Pulled By: rickhanlonii

fbshipit-source-id: b697e3346a863d1b130881592b0522a96c202b63

RNTester/js/DatePickerAndroidExample.js

@@ -21,10 +21,25 @@ const {
 const RNTesterBlock = require('./RNTesterBlock');
 const RNTesterPage = require('./RNTesterPage');
 
-class DatePickerAndroidExample extends React.Component {
-  static title = 'DatePickerAndroid';
-  static description = 'Standard Android date picker dialog';
+type Props = $ReadOnly<{||}>;
+type State = {|
+  presetDate: Date,
+  simpleDate: Date,
+  spinnerDate: Date,
+  calendarDate: Date,
+  defaultDate: Date,
+  allDate: Date,
+  simpleText: string,
+  spinnerText: string,
+  calendarText: string,
+  defaultText: string,
+  minText: string,
+  maxText: string,
+  presetText: string,
+  allText: string,
+|};
 
+class DatePickerAndroidExample extends React.Component<Props, State> {
   state = {
     presetDate: new Date(2020, 4, 5),
     simpleDate: new Date(2020, 4, 5),
@@ -144,4 +159,13 @@ const styles = StyleSheet.create({
   },
 });
 
-module.exports = DatePickerAndroidExample;
+exports.title = 'DatePickerAndroid';
+exports.description = 'Standard Android date picker dialog';
+exports.examples = [
+  {
+    title: 'Simple date picker',
+    render: function(): React.Element<typeof DatePickerAndroidExample> {
+      return <DatePickerAndroidExample />;
+    },
+  },
+];