RFR: 8342380: Implement JEP draft: Warn about use of Memory-Access Methods in `sun.misc.Unsafe`

[Alan Bateman]

Change default value of the command line option --sun-misc-unsafe-memory-access from "allow" to "warn".

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

Commit messages:
 - Update test
 - Merge branch 'master' into JDK-8342380
 - Update usage/man page
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/21762/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21762&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342380
  Stats: 29 lines in 4 files changed: 10 ins; 5 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/21762.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21762/head:pull/21762

PR: https://git.openjdk.org/jdk/pull/21762