RFR: jextract to spit Array for array type and function layout for callbacks

[Henry Jen]

Hi,

Please review the webrev[1] that will,

- generate Array as carrier type for array instead of java array or Pointer
- make sure NativeCallback functional interface has a function instead of a pointer to function as layout

Cheers,
Henry

[1] http://cr.openjdk.java.net/~henryjen/panama/foreign/jextract_array/webrev/