[foreign-memaccess] RFR: Alternative scalable MemoryScope

[Peter Levart]

This is an alternative MemoryScope which is more scalable when used in a scenario where child scope is frequently
acquired and closed concurrently from multiple threads (for example in parallel Stream.findAny())

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

Commit messages:
 - Alternative scalable MemoryScope

Changes: https://git.openjdk.java.net/panama-foreign/pull/142/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/142/webrev.00
  Stats: 192 lines in 5 files changed: 121 ins; 10 del; 61 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/142.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/142/head:pull/142

PR: https://git.openjdk.java.net/panama-foreign/pull/142