RFR 8171130: jshell tool: /edit adds empty statement.. / 8173007: JShell Tests: ToolFormatTest takes too long

[Robert Field]

Please review...

Bugs:

     jshell tool: /edit adds empty statement to brace terminated snippet
     https://bugs.openjdk.java.net/browse/JDK-8171130

     JShell Tests: ToolFormatTest takes too long
     https://bugs.openjdk.java.net/browse/JDK-8173007

Webrev:

     http://cr.openjdk.java.net/~rfield/8171130v0.webrev/

-Robert