[foreign] RFR 8217989: Consolidate BoundedPointer implementation

[Maurizio Cimadamore]

Hi,
in the light of recent discussions re. access modes, I decided to go 
ahead and cleanup the split between BoundedPointer and 
BoundedMemoryRegion, to avoid duplication of functionalities.

This patch does two things:

* moves Scope, AccessMode on BoundedPointer (where they belong, IMHO)
* reduce BoundedMemoryRegion to a simple helper class used to check 
pointer bounds (and renames it to MemoryBoundInfo)

I also took care of minor cleanups, such as adding better encapsulation 
for pointer/array implementation fields.

Webrev:

http://cr.openjdk.java.net/~mcimadamore/panama/8217989/

Maurizio