RFR: 8337511: Implement JEP-404: Generational Shenandoah (Experimental) [v5]

[William Kemper]

> This PR merges JEP 404, a generational mode for the Shenandoah garbage collector. The JEP can be viewed here: https://openjdk.org/jeps/404. We would like to target JDK24 with this PR.

William Kemper has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 492 commits:

 - Merge remote-tracking branch 'shenandoah/master' into great-genshen-pr-redux
 - Merge
 - 8342560: GenShen: Fix confusing method name
   
   Reviewed-by: ysr
 - 8342564: GenShen: Only reference young/old generation names in generational mode
   
   Reviewed-by: xpeng, ysr
 - Merge remote-tracking branch 'jdk/master' into great-genshen-pr-redux
 - Merge remote-tracking branch 'shenandoah/master' into great-genshen-pr-redux
 - 8342214: GenShen: Reduce code duplication in shFreeSet with iterator abstraction
   
   Reviewed-by: kdnilsen, ysr
 - 8342239: GenShen: Revert changes in adaptive heuristic to avoid overflow on 32 bit
   
   Reviewed-by: ysr
 - 8342278: GenShen: Move non-generational mode test out of generational test configuration
   
   Reviewed-by: ysr
 - 8342255: GenShen: Remove unnecessary enum initial values
   
   Reviewed-by: ysr
 - ... and 482 more: https://git.openjdk.org/jdk/compare/71583222...2a2aa408

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Changes: https://git.openjdk.org/jdk/pull/21273/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21273&range=04
  Stats: 22825 lines in 229 files changed: 21084 ins; 889 del; 852 mod
  Patch: https://git.openjdk.org/jdk/pull/21273.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21273/head:pull/21273

PR: https://git.openjdk.org/jdk/pull/21273