[foreign-memaccess] RFR 8228588: MemoryHandles.varHandle still uses implicit platform endiannes

[Maurizio Cimadamore]

Hi,
in a recent push we removed all implicit endianness from the various 
factories. Now either you go through a factory and provide explicit 
endianness or you pick one of the predefined layout constants.

I noted that one part of the API (MemoryHandles::varHandle) was still 
using implicit endianness (and then internally using 
ByteOrder.nativeOrder()).

This patch gets rid of that:

http://cr.openjdk.java.net/~mcimadamore/panama/8228588/

Now, this makes it a bit more cumbersome when working with 'byte' 
carriers, where ByteOrder doesn't really apply - but I don't think 
there's a lot we can do about that.

Maurizio