RFR: 8377165: G1: Introduce common G1 GC Mark to collect scoped objects

[Thomas Schatzl]

Hi all,

  this change factors out the initial scoped objects common to g1 young and full gc into `G1GCMark` to avoid duplication and ordering issues.

All other scoped objects (maybe but `G1HeapPrinterMark`) are specific to the separate collectors. Not sure it is worth commonalizing them.

Testing: gha

Thanks,
  Thomas

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Commit messages:
 - * fix whitespace
 - * fix copyright
 - 8377165

Changes: https://git.openjdk.org/jdk/pull/29568/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29568&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377165
  Stats: 62 lines in 5 files changed: 21 ins; 29 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/29568.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29568/head:pull/29568

PR: https://git.openjdk.org/jdk/pull/29568