bring back jest-nock support

[zivl]

Unfortunately, due to some race condition or wrong definition, we can't get to run the built-in jest-mock functionality. To remind, it was possible if you're using Jest for testing, all you have to do in your ***.spec.js file is to import the Jest mock as follows:

// some.spec.js
import { testkit } from 'sentry-testkit/dist/jestMock';

test('something', function () {
    // click
    // clack
    // BOOM!
    expect(testkit.reports().length).toBeGreaterThan(0);
});

But we're having issue with that:

1. We're getting errors Sentry is not defined and Maximum call stack size exceeded (looks like circular dep): https://github.com/wix/sentry-testkit/runs/2477315004
2. re-declaring block-scope variables (looks like es imports helps with this, but then we got into first problem): https://github.com/wix/sentry-testkit/pull/78/checks?check_run_id=2826583066

You may refer to the source code of jestMock.ts and we'll be happy for your help and suggestions.

Thank you @sidoruk-sv for pointing this out! 💙