WIP: 8154714: JShell API: addExports support [for Java 9.X]

[Robert Field]

FYI:

JShell javadoc with this change:

     http://cr.openjdk.java.net/~rfield/8154714v4.jshellAPI/

Generated specification difference:

http://cr.openjdk.java.net/~rfield/8154714v4.specdiff/overview-summary.html

-Robert