RFR: Access barriers for arraycopy

[Roman Kennke]

This adds support for arraycopy barriers using the new Access API.
- Add the hooks in a bunch of places where arraycopy is used
- Fix a small issue in the actual Access API
- Make Shenandoah Access barriers apply read- and write-barriers to
the src and dst objects, and re-resolve the actual addresses using
some pointer math.

This should reduce upstream exposure even more.

I'll upstream the changes required to shared code ASAP.

Test: hotspot_gc_shenandoah

http://cr.openjdk.java.net/~rkennke/arraycopy-access-barriers/webrev.00/

ok?