Review request: JDK-8157246 MHs.arrayLength, arrayElementGetter/Setter, arrayConstructor need to specify invocation-time behavior

[mandy chung]

http://cr.openjdk.java.net/~mchung/jdk10/webrevs/8157246/webrev.00/index.html
This fixes the spec of MethodHandles::arrayLength, arrayConstructor, 
arrayElementGetter/Setter to specify the behavior if the returned method 
handle is invoked with null array or invalid index; same runtime 
exception thrown by the bytecode behavior.  MethodHandle::asSpreader 
spec is also clarified to throw NPE and IAE except when it spreads with 
no argument and the returned method handle accepts a zero-length array 
or null array.

Thanks
Mandy