[foreign-memaccess+abi] RFR: Add exhaustive test for resource scope handle

[Maurizio Cimadamore]

During some recent benchmarking, we have identified an issue where acquiring/closing a scope handle on an implicit scope was not working as expected, and was throwing an NPE instead.
This patch adds a test which acquires 5 handles (recursively), and then release them.
It checks all the different scope variants, and, for each acquired handle it also tests for idempotency.

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Commit messages:
 - Merge branch 'foreign-memaccess+abi' into scope-handle-test
 - Add test for recursive acquires
 - Add test for scope handles
 - Initial push

Changes: https://git.openjdk.java.net/panama-foreign/pull/504/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=504&range=00
  Stats: 38 lines in 1 file changed: 38 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/504.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/504/head:pull/504

PR: https://git.openjdk.java.net/panama-foreign/pull/504