[JSTEP-10] migrate hppc, eclipse-collections, pcollections to JUnit 5

[JooHyukKim]

part of #174
These modules are small enough to bundle up in one PR.
guava module will follow.

[cowtowncoder]

Thanks @JooHyukKim ! Merged to 2.19, master.

[JooHyukKim]

Thanks!
Will try to do the rest tonight 👌🏽
Been caught up with adjusting to new work environment 🥲

[cowtowncoder]

@JooHyukKim No rush. We are making good progress. I need to write a doc/Discussion about specific goals for getting 3.0.0-SNAPSHOT done by mid/late February and while JUnit conversion is not a must, it's good to get it mostly done by then.