RFR: 8338535: GenShen: some style improvements to source code implementation

[William Kemper]

Clean backport

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

Commit messages:
 - Backport 07c540d96592c150ba99ec8c08d4dbcb85f0c7e0

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/87/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=87&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338535
  Stats: 112 lines in 16 files changed: 66 ins; 10 del; 36 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/87.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/87/head:pull/87

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/87