RFR: 8320710: Adjust heap size when close to compressed oops limit [v2]

[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

Oli Gillespie has updated the pull request incrementally with one additional commit since the last revision:

  Don't adjust heap when compressed oops explicitly disabled, fix tests

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/16813/files
  - new: https://git.openjdk.org/jdk/pull/16813/files/8a4e4c11..5b403413

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=16813&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=16813&range=00-01

  Stats: 15 lines in 2 files changed: 10 ins; 0 del; 5 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