Mock Linking - openURL & canOpenURL

Summary:
This PR brings 2 basic mocks for `Linking`'s `openURL` & `canOpenURL` methods. Below you can find 2 examples on how to it works.

```javascript

  it('presses the open website button', () => {
    const wrapper = shallow(<Info />);

    expect(wrapper).toBeDefined();

    wrapper.find('TouchableOpacity').simulate('press');

    expect(Linking.openURL).toHaveBeenCalledTimes(1);
    expect(Linking.openURL).toHaveBeenCalledWith('https://www.hello.world/');
  });

  it('presses the call button', () => {
    const wrapper = shallow(<MoreInfo />);

    expect(wrapper).toBeDefined();

    wrapper.find('TouchableOpacity').simulate('press');

    expect(Linking.canOpenURL).toHaveBeenCalledTimes(1);
    expect(Linking.canOpenURL).toHaveBeenCalledWith('tel:01273123123');
  });
````
Closes https://github.com/facebook/react-native/pull/12839

Differential Revision: D4908903

Pulled By: javache

fbshipit-source-id: 0b62e9c2a7f920dc8bf0a49c1973f65c473eb653

jest/setup.js

@@ -131,6 +131,12 @@ const mockNativeModules = {
     addListener: jest.fn(),
     removeListeners: jest.fn(),
   },
+  Linking: {
+    openURL: jest.fn(),
+    canOpenURL: jest.fn(
+      () => new Promise((resolve) => resolve(true))
+    ),
+  },
   LocationObserver: {
     getCurrentPosition: jest.fn(),
     startObserving: jest.fn(),