[foreign-memaccess] RFR 8235259: Java layout constants should use native endianness

[Maurizio Cimadamore]

As discussed in [1, 2], this patch changes the endiannes polarity of 
JAVA_XYZ layout constants from big endian to native endian.

The move comes as a consequence of the realization that we want these 
constants to allow for interop with Java arrays - e.g. JAVA_INT should 
eventually become Integer::LAYOUT.

Webrev:

http://cr.openjdk.java.net/~mcimadamore/panama/8235259/

Cheers
Maurizio

[1] - 
https://mail.openjdk.java.net/pipermail/panama-dev/2019-November/006737.html
[2] - 
https://mail.openjdk.java.net/pipermail/panama-dev/2019-December/006785.html