RFR: 8325082: Rename headers named 'heapRegion*' of G1

[Lei Zaakjyu]

8325082: Rename headers named 'heapRegion*' of G1

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Commit messages:
 - rename

Changes: https://git.openjdk.org/jdk/pull/17666/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17666&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325082
  Stats: 267 lines in 105 files changed: 46 ins; 46 del; 175 mod
  Patch: https://git.openjdk.org/jdk/pull/17666.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17666/head:pull/17666

PR: https://git.openjdk.org/jdk/pull/17666