Add Object::Get/SetField methods for 8 and 16 bit fields.

For simplicity new methods lack support for transactions.
Those new netods are used to implement sun.misc.Unsafe.get/set
methods for 8/16 bit wide primitives. Those methods are used
by the java primitive serialization/deserialization methods.

Change-Id: Iaa133b32beac996642f691e1611536f5fd11a260