Fix mock for TextInput (facebook#28332)

Summary:
This PR adds the `isFocused` method to the mock of the TextInput component. My understanding some of the latest changes on the TextInput to make it use a forwardRef change the way this method is mock giving an error when trying to use in on a mock.
The change suggested here fixes the issue.

## Changelog

[JavaScript] [Fixed] - Fix the mock for TextInput to support the `isFocused` method
Pull Request resolved: facebook#28332

Reviewed By: cpojer

Differential Revision: D20538044

Pulled By: TheSavior

fbshipit-source-id: be734af105ab62ffdf9ed4017bd70845e207f8cd

jest/setup.js

@@ -89,10 +89,12 @@ jest
     mockComponent('../Libraries/Text/Text', MockNativeMethods),
   )
   .mock('../Libraries/Components/TextInput/TextInput', () =>
-    mockComponent(
-      '../Libraries/Components/TextInput/TextInput',
-      MockNativeMethods,
-    ),
+    mockComponent('../Libraries/Components/TextInput/TextInput', {
+      ...MockNativeMethods,
+      isFocused: jest.fn(),
+      clear: jest.fn(),
+      getNativeRef: jest.fn(),
+    }),
   )
   .mock('../Libraries/Modal/Modal', () =>
     mockComponent('../Libraries/Modal/Modal'),