Migrate tests from Junit4 to Junit5

[Desislav-Petrov]

Work scope

Currently, all modules of eclipse collections use junit4 and as advised by @donraab we should move to junit5.

The migration will be done in a multi-stage approach to avoid a single massive PR that's difficult to review.

Breakdown of tasks

The work will be broken down in 3 PRs.

• Introduce junit5 vintage & jupiter engines to replace junit4 and migrate the main unit-tests module to junit5 - PR-1576
• Migrate all remaining modules to junit 5 - More detailed explanation in a new issue and PR to come soon
• Clean up any remaining items & remove the junit5 vintage engine - More detailed explanation in a new issue and PR to come soon

I plan to execute the full migration so happy to have the ticket assigned to me.