Migrate TestProjectionViewer and the other tests in this plug-in to Junit5

[vogella]

During review of @danthe1st changes I notice that the tests are still using JUnit4. Once I finished reviewing the #3456 I plan to migrate the rest of the tests.

@danthe1st I hope this will not interfere with any planned work from you?

[danthe1st]

I hope this will not interfere with any planned work from you?

No. And even if you are migrating the tests to JUnit 5 first, I can update my PR.