Jest testing not possible with CommentsRepository premium plugin

[stefanseeger]

Suggested merge commit message (convention)

Docs: Enhance jest testing section to work with CommentsRepository. Closes #17421.

---

Additional information

📝 Provide a description of requested docs changes

The jest related docs for angular, react and vue are not working when the premium plugin CommentsRepository is used

Error message

FrontEnd\node_modules\@ckeditor\ckeditor5-collaboration-core\dist\index.js:392
    const _0x27ffc6 = _0x20b54e['getClientRects']()['item'](0x0);
                                                           ^

TypeError: _0x20b54e.getClientRects(...).item is not a function
    at R (FrontEnd\node_modules\@ckeditor\ckeditor5-collaboration-core\dist\index.js:392:60)
    at r._getTargetForId (FrontEnd\node_modules\@ckeditor\ckeditor5-comments\dist\index.js:22:176593)     
    at d._target (FrontEnd\node_modules\@ckeditor\ckeditor5-comments\dist\index.js:22:178362)
    at d._getNormalizedTarget (FrontEnd\node_modules\@ckeditor\ckeditor5-comments\dist\index.js:22:54176) 
    at new d (FrontEnd\node_modules\@ckeditor\ckeditor5-comments\dist\index.js:22:52317)
    at o._attachCommentThread (FrontEnd\node_modules\@ckeditor\ckeditor5-comments\dist\index.js:22:137698)
    at ie.attachTo (FrontEnd\node_modules\@ckeditor\ckeditor5-comments\dist\index.js:22:154306)
    at FrontEnd\node_modules\@ckeditor\ckeditor5-comments\dist\index.js:22:178334
    at processTicksAndRejections (node:internal/process/task_queues:95:5)

Fix

Additional mocking for Element.prototype.getClientRects is needed