[foreign-memaccess] RFR: Move MemoryAddress::copy (more review feedback)

[Maurizio Cimadamore]

This simple patch addresses some of the review feedback from Paul (sorry for having integrated too soon!).

Cheers

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Commit messages:
 - Address review feedback

Changes: https://git.openjdk.java.net/panama-foreign/pull/172/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/172/webrev.00
  Stats: 13 lines in 3 files changed: 0 ins; 1 del; 12 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/172.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/172/head:pull/172

PR: https://git.openjdk.java.net/panama-foreign/pull/172