RFR: 8367450: Shenandoah: Log the composition of the collection set [v3]

[William Kemper]

> Reuse the same log message from GenShen which details the composition of the live data to be evacuated. In the non-generational modes, all regions are considered young and nothing will be promoted (or old).

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

  Restore accidentally deleted constructor

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Changes:
  - all: https://git.openjdk.org/jdk/pull/27235/files
  - new: https://git.openjdk.org/jdk/pull/27235/files/14d36331..7bde84b8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27235&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27235&range=01-02

  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27235.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27235/head:pull/27235

PR: https://git.openjdk.org/jdk/pull/27235