[foreign-abi] RFR: Merge foreign-memaccess

[Maurizio Cimadamore]

This is a trivial merge of the TestSegments test which had some conflicts due to import statements.

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Commit messages:
 - Trivial merge of TestSegments
 - JDK-8242051: Clarify difference between checked and unchecked addresses

Changes: https://git.openjdk.java.net/panama-foreign/pull/94/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/94/webrev.00

The following webrevs contain only the adjustments done while merging with regards to each parent branch:
 - foreign-abi: https://webrevs.openjdk.java.net/panama-foreign/94/webrev.00.0
 - foreign-memaccess: https://webrevs.openjdk.java.net/panama-foreign/94/webrev.00.1

  Stats: 53 lines in 6 files changed: 25 ins; 3 del; 25 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/94.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/94/head:pull/94

PR: https://git.openjdk.java.net/panama-foreign/pull/94