RFR: 8366688: G1: Rename G1HeapRegionRemSet::is_added_to_cset_group() to has_cset_group()

[Thomas Schatzl]

Hi all,

  please review this trivial renaming of `G1HHRS::is_added_to_cset_group` - it's just misnamed, we never add G1HRRS to the cset groups.

Testing: gha, local compilation

Thanks,
  Thomas

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Commit messages:
 - * copyright update
 - 8366688

Changes: https://git.openjdk.org/jdk/pull/27048/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27048&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366688
  Stats: 18 lines in 8 files changed: 0 ins; 0 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/27048.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27048/head:pull/27048

PR: https://git.openjdk.org/jdk/pull/27048