Add a trivial kotlin test to LibcoreCtsTestCases.

This test just proves that test code written in kotlin and using the
kotlin standard library can be executed on the device. (It may well be
reverted once enough kotlin is around that this is no longer in
question.)

Bug: 73281388
Test: cts-tradefed run cts-dev -m CtsLibcoreTestCases -t libcore.example (also tested that it fails without the @Ignore on the failing test)
Change-Id: Id49802abc4ba2cfd9a971693ef2853f4e54e8b77