8245585: Add SourceVersion.RELEASE_16
8245586: Add source 16 and target 16 to javac
8245544: com/sun/tools/javac/platform/JDKPlatformProvider.java does not support ct.sym with platform versions 16+
Co-authored-by: David Holmes <david.holmes@oracle.com>
Co-authored-by: Jan Lahoda <jan.lahoda@oracle.com>
Reviewed-by: erikj, dholmes, ihse, neugens, jjg, jlahoda, jlaskey, mikael
