feat: add method which return current cdp

[PavelMor25]

Purpose

closes Devexpress/testcafe-private/issues/479

Approach

Describe how your changes address the issue or implement the desired functionality in as much detail as possible.

References

Provide a link to the existing issue(s), if any.

Pre-Merge TODO

• Write tests for your proposed changes
• Make sure that existing tests do not fail

[Aleksey28]

Please, look at my comments. After that update type definitions here https://github.com/DevExpress/testcafe/tree/master/ts-defs-src

[Aleksey28]

Please, look at my comments, and also add definition tests to this directory: https://github.com/DevExpress/testcafe/blob/master/test/server/compiler-test.js
As example, you can explore how it was made for getCurrentWindow.