Playwright code coverage structure

[sh977218]

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Bug description:

This is not a bug report, but more like a code refectory.
In e2e-app's playwright global setup function, it actually returns a function, which will run during global teardown, as documented by playwright. I spent quite some time to figure that out.
I think having a more straightforward two separated playwright file, global setup and teardown, would help others understood easier.
I'm happy to pull a PR to do this fix. If I can get an affirmative response first.

Link to minimally-working StackBlitz that reproduces the issue:

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https://github.com/ng-bootstrap/ng-bootstrap#you-think-youve-found-a-bug

Versions of Angular, ng-bootstrap and Bootstrap:

Angular:

ng-bootstrap:

Bootstrap: