feat: junit standalone - Githubissues

This PR contains the fundamental changes.

mvn and gradle commands are used as utilitary commans to obtain the dependency jars
compiles using java and javac
runs tests using the junit cli
Adds :NeotestJava setup to download the junit jar from https://mvnrepository.com/artifact/org.junit.platform/junit-platform-console-standalone
Adds documented config in case you want to place it in a different directory or a different version

rcasia / neotest-java