JDK 12 RFR of JDK-8206085 : Refactor langtools/tools/javac/versions/Versions.java

[joe darcy]

Hello,

Fresh off of updating

     langtools/tools/javac/versions/Versions.java

for the JDK 11 -> 12 transition, I'd like to refactor the test to reduce 
the maintenance needed when adding new versions (as in new releases) or 
removing versions (as is planned for later in JDK 12):

     http://cr.openjdk.java.net/~darcy/8206085.0/

Thanks,

-Joe