8205621: Increment JDK version for JDK 12
8193292: Add SourceVersion.RELEASE_12
8193290: Add source 12 and target 12 to javac
8205619: Bump maximum recognized class file version to 56 for JDK 12
Co-authored-by: Erik Joelsson <erik.joelsson@oracle.com>
Co-authored-by: Mikael Vidstedt <mikael.vidstedt@oracle.com>
Reviewed-by: alanb, smarks, jjg, mr, erikj, psandoz, dholmes