RFR: 8348171: Refactor GenerationCounters and its subclasses

Tue Jan 21 09:57:15 UTC 2025

Simple refactoring of removing the use of `virtual` method and use concrete subclasses when needed.

Test: tier1-5

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Commit messages:
 - gen-counter

Changes: https://git.openjdk.org/jdk/pull/23209/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23209&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348171
  Stats: 195 lines in 16 files changed: 8 ins; 157 del; 30 mod
  Patch: https://git.openjdk.org/jdk/pull/23209.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23209/head:pull/23209

PR: https://git.openjdk.org/jdk/pull/23209