[code mining] Consider adding JUnit minings / debugging minings

The original code mining repo, https://github.com/angelozerr/jdt-codemining, has a few more tricks than the current JDT. Namely,

- JUnit minings for running specific tests, seeing their status: https://github.com/angelozerr/jdt-codemining/tree/master/org.eclipse.jdt.codemining/src/org/eclipse/jdt/experimental/junit/codemining
- an incredible debug mining showing variable values inline, https://github.com/angelozerr/jdt-codemining/tree/master/org.eclipse.jdt.codemining/src/org/eclipse/jdt/experimental/debug/ui/codemining
- (and `var` local inference type, https://github.com/angelozerr/jdt-codemining/tree/master/org.eclipse.jdt.codemining/src/org/eclipse/jdt/experimental/ui/javaeditor/codemining/var, already requested by https://github.com/eclipse-jdt/eclipse.jdt.ui/issues/329)

Are we considering adding any of those? I'd gladly help with asking for permission from the original author, if needed, and integrating the cleaned-up code into JDT if that helps in any way.

Start by reviewing the linked jdt-codemining paths for the JUnit and debug implementations, then compare them with the current JDT code-mining support. Confirm whether the original author’s permission is needed and document the scope and integration requirements for any selected mining; done means there is an agreed implementation path.

Written by the indexing model from the issue text.