RFR 8153920: jshell tool: allow a parameter on the /vars /methods /classes commands

[Robert Field]

Please review that allows the same parameters on /vars /methods and 
/types as allowed on /list -- thus one can look a specific snippet in 
detail:   /var x

Bug:
     https://bugs.openjdk.java.net/browse/JDK-8153920

Webrev:
     http://cr.openjdk.java.net/~rfield/8153920v0.webrev/

Thanks,
Robert