[foreign-abi] RFR: 8248499: Add methods to allocate off heap arrays from Java arrays [v3]

[Maurizio Cimadamore]

> This patch adds methods to NativeScope which allow clients to allocate off-heap arrays from Java on-heap arrays.
> 
> While in most cases the code for copying is straightforward, we have to take into account endianness mismatches (in
> case the user wants to store the array elements off-heap in an endianness that doesn't match that of the platform).
> To allow for that, I've added a new implementation method in AbstractMemorySegmentImpl, which is the same as
> `copyFrom`, but adds the byte swap (a wrapper around `Unsafe::copySwapMemory`).

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Addressed review comments

-------------

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/222/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/222/files/38c81345..86c572f3

Webrevs:
 - full: https://webrevs.openjdk.java.net/panama-foreign/222/webrev.02
 - incr: https://webrevs.openjdk.java.net/panama-foreign/222/webrev.01-02

  Stats: 69 lines in 1 file changed: 6 ins; 50 del; 13 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/222.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/222/head:pull/222

PR: https://git.openjdk.java.net/panama-foreign/pull/222