Fix zero after
JDK-8169881, JDK-8175318, JDK-8178350
JDK-8169881 (Remove implicit Handle conversions oop->Handle): missed fixing up a number of places in bytecodeInterpreter.cpp.
JDK-8175318 (Performance issue regarding local JNI references): removed JNIHandleBlock::clear() as unused, but it was still used in the CppInterpreter. Reintroduced clear(), but left private, as CppInterpreter is friend.
JDK-8178350: klassVtable and klassItable should be ValueObj: missed an occurence of klassVtable* in methodHandles_zero.cpp.