feat: jest integration

[kirillzyusko]

📜 Description

Will fix #101

💡 Motivation and Context

Right now it's not possible to write jest tests for components, that are using this library. To overcome the limitation I added mock and wrote several test cases as examples.

📢 Changelog

CI

• run example tests;

Docs

• added section about testing;

Jest

• added mocks;
• added example of tests;

🤔 How Has This Been Tested?

Tested locally and on CI that tests are working fine.

📝 Checklist

• CI successfully passed

[IvanIhnatsiuk]

maybe it's better to split these object to fisrtPosition, secondPosition, thirdPosition?

const thirdPosition = {
      height: new Animated.Value(300),
      progress: new Animated.Value(1),
      };
      
 (useKeyboardAnimation as jest.Mock).mockReturnValue(thirdPosition);