[jdk21u-dev] RFR: 8322279: Generational ZGC: Use ZFragmentationLimit and ZYoungCompactionLimit as percentage instead of multiples

[Liang Mao]

This commit fixed incorrect use of production options of generational ZGC. Since JDK21 is the only LST version with generational ZGC， we need to fix the potential bugs.
Additional testing on fastdebug against test/hotspot/jtreg/gc/z

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Commit messages:
 - Backport bf813be0f30391c67de3ea74c7522d7cbb8d3c3b

Changes: https://git.openjdk.org/jdk21u-dev/pull/173/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=173&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8322279
  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/173.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/173/head:pull/173

PR: https://git.openjdk.org/jdk21u-dev/pull/173