[foreign] RFR: Pointer (and other) API refresh

[Maurizio Cimadamore]

Hi,
this change updates most of the public APIs to reflect the changes 
discussed in the document [1].

There are many changes here, let's go one by one:

* Pointer API has been updated and the Reference class has been removed

* the top type for native structs used to be Reference, now is Struct

* the Resource interface has been parameterized

* few changes to the Scope API - and also consolidated the Scope 
implementation in order to remove code duplication between HeapScope and 
NativeScope

* Refresh of LayoutType - as per [1], the new version of LayoutType is 
MH-based; these MH handles are used in codegen (see changes in 
HeaderImplGenerator and StructImplGenerator)

* Added NativeTypes public class to add useful LayoutType constants

* The removal of the Reference class also required some jextract tweak - 
more specifically, the xyz$ref methods have been replaced by xyz$ptr 
method (which return pointer of given field). This is also consistent 
with [1].

* The Qsort test has been updated, fixed and un-ignored

* most of the public API now have full javadoc (yayy!)

While this change greatly improves the public API, much remains to be 
done internally; I counter 5 (!!) different ways in which Java values 
are 'loaded/stored' from/to memory/registers:

1) regular struct access
2) array struct access
3) global variable access
4) function invocation
5) callback invocation

Some consolidation is badly needed here - as in each of these places, 
the system will perform the task in a slightly different way; for 
instance one Java carrier might be supported in (1), but not in (3). 
Also in some places we depend on the layout (e.g. global vars and struct 
access) while in other places (function call and callbacks) we infer 
layouts from Java signatures, which is IMHO a bad smell (e.g. a function 
that return a Pointer<Character> doesn't necessarily means it's 
returning a pointer to a 16-bit value).

Much more work is needed in the impl internals, in order to reduce 
duplication between paths and improve regularity.

Webrev here:

http://cr.openjdk.java.net/~mcimadamore/panama/api-refresh/

[1] - http://cr.openjdk.java.net/~mcimadamore/panama/panama-binder-v3.html