RFR: 8256299: Implement JEP 396: Strongly Encapsulate JDK Internals by Default

[Mark Reinhold]

Please review this implementation of JEP 396 (https://openjdk.java.net/jeps/396).
Alan Bateman is the original author; I’ve credited him in the commit metadata.
Passes tiers 1-3 on {linux,macos,windows}-x64 and linux-aarch64.

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Commit messages:
 - 8256299: Implement JEP 396: Strongly Encapsulate JDK Internals by Default

Changes: https://git.openjdk.java.net/jdk/pull/1324/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1324&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8256299
  Stats: 161 lines in 6 files changed: 22 ins; 76 del; 63 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1324.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1324/head:pull/1324

PR: https://git.openjdk.java.net/jdk/pull/1324