Move Java9LanguageFeaturesTest into its own directory.

This is in preparation for http://r.android.com/999933, which adds
more build file complexity around this test, and means that complexity
is kept out of the top-level libcore JavaLibrary.bp.

Test: cts-tradefed run cts-dev -m CtsLibcoreTestCase -t libcore.libcore.internal

Change-Id: I31bb233925cfb39c0654b0af0813b33b26527787
3 files changed