Create a stand-alone test launcher for runnig ORT tests

[sschuberth]

For cases where one would like to know whether ORT would run successfully in a certain environment (like a Docker container), it would be nice to have a way to run all ORT tests (esp. the funTest ones) from a self-contained binary, without the need to build ORT from sources or to use Gradle.

One idea for implementing this is via a combination of the Gradle application / JIB plugins and an approach as discussed here, plus using JUnits's console launcher as the entry point for the Docker image.