RFR: 8337511: Implement JEP-404: Generational Shenandoah (Experimental) [v4]

[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 487 commits:

 - 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
 - 8342001: GenShen: Factor cases for allocation type into separate methods
   
   Reviewed-by: ysr, kdnilsen
 - 8341992: GenShen:  Fix formatting, remove unreachable code, unused imports and unnecessary comments
   
   Reviewed-by: ysr
 - Merge
 - Merge remote-tracking branch 'jdk/master' into great-genshen-pr-redux
 - Fix merge error
 - ... and 477 more: https://git.openjdk.org/jdk/compare/3da68900...b3e4b4ca

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

Changes: https://git.openjdk.org/jdk/pull/21273/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21273&range=03
  Stats: 22819 lines in 229 files changed: 21077 ins; 890 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