RFR: 8367473: Shenandoah: Make the detailed evacuation metrics a runtime diagnostic option [v5]

[William Kemper]

> Non-product builds currently have a feature to produce detailed metrics about evacuations (number of objects, number of bytes, split out by age (young, old, promotion) and thread (mutator or worker). This change makes this feature accessible in release builds as a diagnostic option.

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Only print promotion/old evacuation metrics in generational mode

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27238/files
  - new: https://git.openjdk.org/jdk/pull/27238/files/0e1446de..0ab56c91

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27238&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27238&range=03-04

  Stats: 4 lines in 1 file changed: 2 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/27238.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27238/head:pull/27238

PR: https://git.openjdk.org/jdk/pull/27238