[foreign] RFR: cleanup Pointer API

[Maurizio Cimadamore]

Hi,
in preparation for the changes to the pointer API outlined in [1], 
here's a cleanup that removes the methods from the Pointer interface 
that are only required to support code generation.

These methods are now moved into a new class, called RuntimeSupport. 
I've tweaked the HeaderImplGenerator class to perform indirect access to 
these method, through a bunch of static MH fields (this is to avoid 
access errors due to module boundaries).

Webrev:

http://cr.openjdk.java.net/~mcimadamore/panama/pointer-cleanup/

Maurizio