[foreign-memaccess+abi] RFR: 8267989: Exceptions thrown during upcalls should be handled

[Jorn Vernee]

Hi,

This patch regularizes exception handling for exceptions thrown during upcalls. Exceptions thrown during upcalls are now always handled by printing out the stack trace and then calling `System::exit` (see the JBS issue for some motivation).

I've added some documentation for the exception handling to `CLinker::upcallStub`, as well as a new public `int` constant in `CLinker` which is the error code that is passed to `System::exit`. The returned error code can also be configured by a system property, which for now is mostly useful for testing purposes to make sure we don't get a consistent false positive.

Thanks,
Jorn

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

Commit messages:
 - Use priviledgedGetProperty instead of Integer.getInteger
 - Fix test and add documentation + ERR_UNCAUGHT_EXCEPTION
 - Add tests
 - Handle exception uniformly across upcall modes

Changes: https://git.openjdk.java.net/panama-foreign/pull/543/files
 Webrev: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=543&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267989
  Stats: 191 lines in 6 files changed: 188 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/543.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/543/head:pull/543

PR: https://git.openjdk.java.net/panama-foreign/pull/543