RFR: 8337511: Implement JEP-404: Generational Shenandoah (Experimental) [v3]

[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 478 commits:

 - Fix merge error
 - Merge remote-tracking branch 'jdk/master' into great-genshen-pr-redux
 - Merge remote-tracking branch 'jdk/master' into great-genshen-pr-redux
 - Merge branch 'shenandoah/master' into great-genshen-pr-redux
 - Merge
 - 8341099: GenShen: assert(HAS_FWD == _heap->has_forwarded_objects()) failed: Forwarded object status is sane
   
   Reviewed-by: kdnilsen
 - 8341485: GenShen: Make evac tracker a non-product feature and confine it to generational mode
   
   Reviewed-by: kdnilsen, ysr
 - Merge
 - 8341042: GenShen: Reset mark bitmaps for unaffiliated regions when preparing for a cycle
   
   Reviewed-by: kdnilsen
 - 8339616: GenShen: Introduce new state to distinguish promote-in-place phase as distinct from concurrent evacuation
   
   Reviewed-by: kdnilsen, shade, ysr
 - ... and 468 more: https://git.openjdk.org/jdk/compare/b9db74a6...4db1e0e1

-------------

Changes: https://git.openjdk.org/jdk/pull/21273/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21273&range=02
  Stats: 22593 lines in 229 files changed: 20952 ins; 810 del; 831 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