RFR: 8338479: GenShen: Detemplatize ShenandoahScanRemembered

[William Kemper]

Clean backport

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

Commit messages:
 - Backport 78277f9f6e61ecc61eddd3fa72d963f08d7e754f

Changes: https://git.openjdk.org/shenandoah-jdk21u/pull/85/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah-jdk21u&pr=85&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338479
  Stats: 1216 lines in 10 files changed: 545 ins; 625 del; 46 mod
  Patch: https://git.openjdk.org/shenandoah-jdk21u/pull/85.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah-jdk21u.git pull/85/head:pull/85

PR: https://git.openjdk.org/shenandoah-jdk21u/pull/85