Export Modal’s Flow types (#25554)

Summary:
I'd like to use `Modal`’s flow types in my application to make a reusable component.

## Changelog

[JavaScript] [Added] - Exported `Modal`’s types
Pull Request resolved: #25554

Test Plan: n/a

Differential Revision: D16180231

Pulled By: cpojer

fbshipit-source-id: 9cfd5163a187954783102bfe4d9b4d1dbc8c6e6d

Author: swashcap

Libraries/Modal/Modal.js

@@ -42,13 +42,13 @@ import type {SyntheticEvent} from '../Types/CoreEventTypes';
 // destroyed before the callback is fired.
 let uniqueModalIdentifier = 0;
 
-type OrientationChangeEvent = SyntheticEvent<
+export type OrientationChangeEvent = SyntheticEvent<
   $ReadOnly<{|
     orientation: 'portrait' | 'landscape',
   |}>,
 >;
 
-type Props = $ReadOnly<{|
+export type Props = $ReadOnly<{|
   ...ViewProps,
 
   /**