[foreign-abi] RFR: Merge foreign-memaccess

[Maurizio Cimadamore]

Just move the newly added ForeignUnsafe::asUnconfined to the new Foreign class.

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

Commit messages:
 - Merge foreign-memaccess
 - JDK-8241849: Add unsafe way to create unconfined memory segment view

Changes: https://git.openjdk.java.net/panama-foreign/pull/76/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/76/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/76/webrev.00.0
 - foreign-memaccess: https://webrevs.openjdk.java.net/panama-foreign/76/webrev.00.1

  Stats: 47 lines in 4 files changed: 46 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/76.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/76/head:pull/76

PR: https://git.openjdk.java.net/panama-foreign/pull/76