[jdk21u] RFR: 8314990: Generational ZGC: Strong OopStorage stats reported as weak roots

[Aleksey Shipilev]

Clean and trivial backport to improve ZGC diagnostics.

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Commit messages:
 - Backport dcd6e756718b656d43f4575558f41ce0c28d0eca

Changes: https://git.openjdk.org/jdk21u/pull/421/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk21u&pr=421&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314990
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk21u/pull/421.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u.git pull/421/head:pull/421

PR: https://git.openjdk.org/jdk21u/pull/421