8157160: JSON.stringify does not work on ScriptObjectMirror objects
Reviewed-by: hannesw, mhaupt
{"foo":42}
[5,6,76,7]
"hello"
{"name":"nashorn","versions":["es5.1","es6"]}
true
{"x":42,"y":"hello"}
"my json representation"
"value from toJSON function"
{"foo":"HELLO"}