Junit 6 support

[cdietrich]

we use junit 5 in

• bom (can have only one version
• manifests (or testing library, would we need a range)
• wizard that creates maven, tycho, gradle and plain plugin projects

=>

• option 1: drop 5, replace with 6
• option 2: find a way to support both without ending up with sth like ClassCastException when running tests with JUnit 6 #3552

cc @szarnekow @HannesWell @iloveeclipse @LorenzoBettini

feel free to add

[iloveeclipse]

FYI: Simeon will check the state of #3560, let see how far this goes.

[trancexpress]

My understanding is that we proceed with option 1, replacing JUnit 5 support with JUnit 6.

[iloveeclipse]

My understanding is that we proceed with option 1, replacing JUnit 5 support with JUnit 6.

Correct.

[cdietrich]

xtext/xtext-reference-projects#537

[trancexpress]

This one also: eclipse-xtext/xtext-website#117

[cdietrich]

done