RFR: 8344264: GenShen: Improve comments and method names

[William Kemper]

More hygiene for GenShen.

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Commit messages:
 - Improve method names and comments

Changes: https://git.openjdk.org/shenandoah/pull/539/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=539&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344264
  Stats: 15 lines in 7 files changed: 4 ins; 0 del; 11 mod
  Patch: https://git.openjdk.org/shenandoah/pull/539.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/539/head:pull/539

PR: https://git.openjdk.org/shenandoah/pull/539