RFR: 8294844: Improve G1 young gen length revise trigger

[Thomas Schatzl]

Hi all,

  please review this change that makes actual young gen length revising unconditional.

This solves the following issues:
* currently young gen revising would only shrink the young gen, which would waste time available in the pause.
* young gen sizing is not only dependent on remembered sets (it has been gated on changes to the remembered set only) but also significantly on the pending cards length. This means that in some cases necessary revising would not occur, being a cause for greatly missing pause times.

Depends on PR#10651, please review that one first.

Testing: Testing: gha, local testing, tier1-5 with other changes in this patch series, perf testing with other changes in this patch series

Thanks,
  Thomas

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Depends on: https://git.openjdk.org/jdk/pull/10651

Commit messages:
 - young gen revise trigger initial version

Changes: https://git.openjdk.org/jdk/pull/10652/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10652&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8294844
  Stats: 38 lines in 3 files changed: 5 ins; 25 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/10652.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10652/head:pull/10652

PR: https://git.openjdk.org/jdk/pull/10652