JDK 12 RFR of JDK-8205615: Start of release updates for JDK 12 / JDK-8193292, JDK-8193290

[joe darcy]

Hello,

With the JDK 11 and 12 split fast approaching [1], it is time to work on 
the various start of release update tasks for JDK 12. Those tasks are 
being tracked under the umbrella bug JDK-8205615: "Start of release 
updates for JDK 12". For JDK 12, we're attempting to get the full set of 
related changes (updated JDK version number, bumped class file version 
update, new javac -source/-target values, etc.) pushed simultaneously. 
This thread is to review the langtools-related portions of the work 
including

     JDK-8193292: Add SourceVersion.RELEASE_12
     JDK-8193290: Add source 12 and target 12 to javac

as well as updates to the langtools tests for the class file update.

Current webrev:

     http://cr.openjdk.java.net/~darcy/8205615.4/

As part of JDK-8193292: "Add SourceVersion.RELEASE_12", the JDK-9 era 
visitors in javax.lang.model.util are updated to state they model over 
version 9 through 12.

For now, tools/javac/options/smokeTests/OptionSmokeTest.java is problem 
listed since it has many hard-coding version checks.

Preview language features are only supported against the current source 
version so those tests need their explicit version number updated.

A handful of test failures still need to be addressed, so there will be 
some minor adjustments to the aggregate set of changes before they are 
pushed.

Thanks,

-Joe

[1] http://mail.openjdk.java.net/pipermail/jdk-dev/2018-June/001462.html