RFR: 8371791: G1: Improve accuracy of G1CollectedHeap::non_young_occupancy_after_allocation()

[Thomas Schatzl]

Hi all,

  please review this change that improves the accuracy of `G1CollectedHeap::non_young_occupancy_after_allocation()` by considering the free space in the old gen retained region.

Testing: tier1-3, gha

Thanks,
  Thomas

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Commit messages:
 - 8371791

Changes: https://git.openjdk.org/jdk/pull/28294/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28294&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371791
  Stats: 13 lines in 3 files changed: 11 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/28294.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28294/head:pull/28294

PR: https://git.openjdk.org/jdk/pull/28294