[jdk21u-dev] RFR: 8321619: Generational ZGC: ZColorStoreGoodOopClosure is only valid for young objects

[Aleksey Shipilev]

Clean backport to fix Generational ZGC.

Picking this up for 21u, @fisk -- tell me if that is not a good idea.

Additional testing:
 - [ ] Linux x86-64 server fastdebug, `hotspot_gc` with `-XX:+UseZGC -XX:+ZGenerational`

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Commit messages:
 - Backport be49dabd0d7e1cd270399849e5353bf33361c4c5

Changes: https://git.openjdk.org/jdk21u-dev/pull/138/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=138&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8321619
  Stats: 31 lines in 3 files changed: 26 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/138.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/138/head:pull/138

PR: https://git.openjdk.org/jdk21u-dev/pull/138