Migrate TestBench to Jakarta EE 9 / Servlet 5.0

[mshabarov]

• change sources to use Servlet 5.0 API, convert packages to jakarta.*
• use JDK 17 as a minimum
• create CI builds: 9.0 branch, snapshot validation build and release build
• migrate to JUnit 5

[knoobie]

And Junit5? ;)

[mshabarov]

Thanks @knoobie , that's a hot topic indeed. I'd include JUnit 5 into this scope as well.

[MarcinVaadin]

As for CI builds - TestBench CI uses single job for running all branches/PRs builds. It will be updated to include maven compiler version property for each build separately, nothing more to be done.

[MarcinVaadin]

As for JUnit5 - common part has been extracted as a part of vaadin/testbench#1318, I've did the same based on current master.

Classes to be migrated to JUnit5:

• RetryRule - can be replaced by https://github.com/artsok/rerunner-jupiter
• ScreenshotOnFailureRule - easily migrated to ScreenshotOnFailureExtension
• ParallelRunner/Scheduler - can we use native JUnit5 or Surefire parallel feature?