[lworld] Dropping jdk.incubator.mvt and MVT change in MethodHandle and reflection

[mandy chung]

http://cr.openjdk.java.net/~mchung/valhalla/webrevs/lworld-drop-mvt

This is the first pass to remove jdk.incubator.mvt module and
MVT support in MethodHandle and reflection.  I have also added
Class::isValue method to determine if it's a value class.  Fields
of a value class are immutable and Field::setXXX methods will
throw IAE if the declaring class is a value class.

Mandy