RFR 8160127, et. al.: JShell API: ExecutionControl implementation support

[Robert Field]

In response to concerns about the logging mechanism, it has been 
removed.  Leaving room the standard logging to be used.
In response to concerns about dependencies on jdk,jshell, 
ExecutionEnv.state() has been removed (this is possible because of the 
JShell-specific logging was removed).
In response to extensibility concerns, there is now 
ExecutionControl.extensionCommand(), a new exception 
ExecutionControl.NotImplementedException, and RemoteCodes returns with 
string commands.
In response to the desire to have additional multiplexed channels and to 
multiplexing, System.out and System.err are no longer special-cased, and 
now symmetric stream maps configure both sides.

Bugs:

     JShell API: extract abstract JDI and abstract streaming 
implementations of ExecutionControl
     https://bugs.openjdk.java.net/browse/JDK-8160127

     JShell API: Reorganize execution support code into 
jdk.jshell.execution (previously sent for review, and combined here)
     https://bugs.openjdk.java.net/browse/JDK-8159935

     JShell API: extract abstract streaming remote agent
     https://bugs.openjdk.java.net/browse/JDK-8160128

Parent bug:

     https://bugs.openjdk.java.net/browse/JDK-8159118

API:

     http://cr.openjdk.java.net/~rfield/jshell_8160127v2/

     Specifically --
http://cr.openjdk.java.net/~rfield/jshell_8160127v2/jdk/jshell/execution/package-summary.html
http://cr.openjdk.java.net/~rfield/jshell_8160127v2/jdk/jshell/spi/package-summary.html

Webrev:

     http://cr.openjdk.java.net/~rfield/8160127v2.webrev/


Thanks,
Robert