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

[Robert Field]

After more review comments --
    Since logging was removed, back-out debugging changes.
    ExecutionControl: Add doc. Add serialVersionUID on exceptions.
    Encapsulate fields in ExecutionControl.ClassBytecodes.
    Optionally configure DirectExecutionControl and its subclasses for 
alternate loader mechanisms with LoaderDelegate.
    JDIExecutionControl: Hide field with map from class name to 
ReferenceType.
    Add testing for aux channel.

Previous code review was v2, this is v4. Please review --

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

     JShell API: Configurable invocation mechanism
     https://bugs.openjdk.java.net/browse/JDK-8159122

Parent bug:

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

API:

     http://cr.openjdk.java.net/~rfield/jshell_8160127v4/

     Specifically --
http://cr.openjdk.java.net/~rfield/jshell_8160127v4/jdk/jshell/execution/package-summary.html
http://cr.openjdk.java.net/~rfield/jshell_8160127v4/jdk/jshell/spi/package-summary.html

Specdiff (v4):

http://cr.openjdk.java.net/~rfield/8160127v4.specdiff/overview-summary.html

Specdiff delta (v2 to v4): Changes, seee below.

http://cr.openjdk.java.net/~rfield/8160127v2v4.specdiff/overview-summary.html

Webrev:

     http://cr.openjdk.java.net/~rfield/8160127v4.webrev/

Webrev delta (v2 to v4):

    http://cr.openjdk.java.net/~rfield/8160127v2v4%2cwebrev/

Thanks,
Robert