Minimal changes make IDEA 2023.2 work out-of-box

Minimal changes make IDEA 2023.2 work out-of-box

Correct maven-compiler-plugin JDK version for IDEA import Compiler bytecode version.

Remove JvstTestRoot's constructor, otherwise IDEA cannot show Run icon aside testMethod.
Another way is adding suite() static method to those classes.

Now we can clone and open project with IDEA 2023.2. Debug single test case with IDEA is very useful.