RFR: 8320710: Adjust heap size when close to compressed oops limit

[Oli Gillespie]

When the heap is between 0 and 2% larger than the compressed oops limit, lower it enough to enable compressed oops. See [issue](https://bugs.openjdk.org/browse/JDK-8320710) for more details.

This is just one way of doing it to show the idea, any other ideas welcome.

Before:

java -Xmx32G -XX:+UseCompressedOops -version
OpenJDK 64-Bit Server VM warning: Max heap size too large for Compressed Oops

After:

java -Xmx32G -XX:+UseCompressedOops -version
OpenJDK 64-Bit Server VM warning: Heap size lowered from 34359738368 to 33822867456 to accommodate Compressed Oops

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Commit messages:
 - Adjust heap size when close to compressed oops limit

Changes: https://git.openjdk.org/jdk/pull/16813/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16813&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320710
  Stats: 18 lines in 1 file changed: 18 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16813.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16813/head:pull/16813

PR: https://git.openjdk.org/jdk/pull/16813