RN: Add @flow to ProgressBarAndroid.js (#39004)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/39004

Adds `flow` to this file. Even thought it is a stub, it still deserves to be checkable by Flow.

Changelog:
[Internal]

Reviewed By: SamChou19815

Differential Revision: D48325186

fbshipit-source-id: a3417bfa12258b85c1eb51744348a1c8aba63a8c

packages/react-native/Libraries/Components/ProgressBarAndroid/ProgressBarAndroid.js

@@ -5,6 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
+ * @flow strict-local
  */
 
 'use strict';