JUnit test discovery integration

[sgammon]

Bazel's default method for running Java tests involves a custom runner and potentially a custom launcher; for native test cases, no launcher is needed at all, but the runner is still needed.

Additionally, GraalVM provides its own runner implementation which discovers JUnit tests in a native binary.

To invoke this code path properly, we probably need to introduce our own runner, which reads the Bazel runner from a new system property (bazel.graalvm.wrapped_testrunner), and then performs the following steps:

• Load the class at bazel.graalvm.wrapped_testrunner, or fallback to default (com.google.testing.junit.runner.BazelTestRunner)
• Read the test suite target from bazel.test_suite
• Invoke initialization steps in org.graalvm.junit.platform.NativeImageJUnitLauncher, or otherwise repeat that code
• Invoke initialization steps and pass control over to the wrapped runner

There is some other ceremony related to testing:

• The native-image build for the test needs --features=org.graalvm.junit.platform.JUnitPlatformFeature
• The runner class will need to be registered for reflection. Since this is dynamic, we will need a Feature for this as well