[foreign-memaccess+abi] RFR: Add exhaustive test for resource scope handle [v2]

[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.

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Simplify test code

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/504/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/504/files/87ee74f6..178b466e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=504&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=504&range=00-01

  Stats: 11 lines in 1 file changed: 0 ins; 5 del; 6 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