RFR: 8365115: G1: Refactor rem set statistics gather code for group

[Thomas Schatzl]

Hi all,

  please review this change to remove some code duplication in group remset statistics gathering.

Testing: gha

Thanks,
  Thomas

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

Commit messages:
 - 8365115

Changes: https://git.openjdk.org/jdk/pull/26691/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26691&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365115
  Stats: 41 lines in 1 file changed: 9 ins; 14 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/26691.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26691/head:pull/26691

PR: https://git.openjdk.org/jdk/pull/26691