Add missing constants to fallback implementation of ToastAndroid (#38803

)

Summary:
Pull Request resolved: #38803

The d.ts file says these constant must exist, but they only exist in the android implementation. This diff stops lying and adds some dummy constants, so that the type will match-up.

Changelog: [Internal]

Reviewed By: yungsters

Differential Revision: D48085126

fbshipit-source-id: 8d5332a71b9b3c1925abeec9e47630a07abf8b86

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

@@ -5,12 +5,20 @@
  * LICENSE file in the root directory of this source tree.
  *
  * @format
- * @noflow
+ * @flow strict-local
  */
 
 'use strict';
 
 const ToastAndroid = {
+  // Dummy fallback toast duration constants
+  SHORT: (0: number),
+  LONG: (0: number),
+  // Dummy fallback toast gravity constants
+  TOP: (0: number),
+  BOTTOM: (0: number),
+  CENTER: (0: number),
+
   show: function (message: string, duration: number): void {
     console.warn('ToastAndroid is not supported on this platform.');
   },