RFR: 8337511: Implement JEP-404: Generational Shenandoah (Experimental) [v2]

[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 incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 475 additional commits since the last revision:

 - 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
 - Merge
 - 8339643: Port JEP 404 to RISC-V
   
   Reviewed-by: wkemper, kdnilsen
 - 8340395: GenShen: Remove unnecessary check on card barrier flag
   
   Reviewed-by: ysr
 - ... and 465 more: https://git.openjdk.org/jdk/compare/143b2cd8...ed16e3ec

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21273/files
  - new: https://git.openjdk.org/jdk/pull/21273/files/8b25abe0..ed16e3ec

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21273&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21273&range=00-01

  Stats: 25330 lines in 433 files changed: 21577 ins; 2314 del; 1439 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