RFR 8199193: jshell tool: Add support for preview features

[Sundararajan Athijegannathan]

* On the new ToolEnablePreviewTest:

1) do you need to build KullTesting for this test?
2) do you need those @module declarations for this test? Seems like this 
test stays within public APIs.

-Sundar

On 23/04/18, 12:10 AM, Robert Field wrote:
> Please review....
>
> Bug:
>
>     https://bugs.openjdk.java.net/browse/JDK-8199193
>
> Webrev:
>
>     http://cr.openjdk.java.net/~rfield/8199193v0.webrev/
>
> Thanks,
> Robert
>
>