RFR: 8344263: GenShen: Reduce extraneous log messages at INFO level [v2]

[William Kemper]

> Genshen logs a lot of fine level detail at `gc=info`. This category should be reserved for major phase changes in the gc cycle.

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

  Log heuristics decisions at info with ergo tag

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

Changes:
  - all: https://git.openjdk.org/shenandoah/pull/540/files
  - new: https://git.openjdk.org/shenandoah/pull/540/files/f02d0245..14a91864

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=540&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=540&range=00-01

  Stats: 28 lines in 3 files changed: 0 ins; 2 del; 26 mod
  Patch: https://git.openjdk.org/shenandoah/pull/540.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/540/head:pull/540

PR: https://git.openjdk.org/shenandoah/pull/540