8168615: JShell API: jdk.jshell.spi should be a pluggable ServiceLoader SPI
Reviewed-by: jlahoda

8160127: JShell API: extract abstract JDI and abstract streaming implementations of ExecutionControl
8159935: JShell API: Reorganize execution support code into jdk.jshell.execution (previously sent for review, and combined here)
8160128: JShell API: extract abstract streaming remote agent
8159122: JShell API: Configurable invocation mechanism
Summary: ExecutionControl implementation support with simplified ExecutionControl interface
Reviewed-by: jlahoda

8131029: JShell: recover from VMConnection launch failure
Reviewed-by: vromero