As discussed in #6682, we should rename all rules and properties which have "JUnit5" as part of their name. JUnit 6 uses the same class names as JUnit 5.

Those are:

• JUnit5TestShouldBePackagePrivate should be renamed to JUnitJupiterTestShouldBePackagePrivate. (The old rule needs to be deprecated)
• JUnit5TestNoPrivateModifier should be renamed to JUnitJupiterTestNoPrivateModifier (No link, because this rule isn't released yet. If we do this before 7.25.0, no deprecation needed. Otherwise see above)
• MethodNamingConventions, property junit5TestPattern should be renamed to junitJupiterTestPattern. (The old attribute needs to be deprecated)