[foreign-memaccess] RFR: Alternative scalable MemoryScope (followup)

[Maurizio Cimadamore]

This simple patch fixes a regression in the byte buffer test (the test was checking for a different exception message).
As I find the new message more informative than the old one, I fixed the test.

I also added some benchmarks to test the new scope (this is already part of the RFR that has been submitted against
jdk/jdk - with few tweaks that I will mirror there).

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Commit messages:
 - * fix exception message check in test

Changes: https://git.openjdk.java.net/panama-foreign/pull/156/files
 Webrev: https://webrevs.openjdk.java.net/panama-foreign/156/webrev.00
  Stats: 46 lines in 2 files changed: 44 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/156.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/156/head:pull/156

PR: https://git.openjdk.java.net/panama-foreign/pull/156