RFR: 8354078: Shenandoah: Make the generational mode be non-experimental (implementation) [v2]

[William Kemper]

> Testing:
> 
> % ./build/linux-x86_64-server-fastdebug/jdk/bin/java -XX:+UseShenandoahGC -XX:ShenandoahGCMode=generational --version
> openjdk 25 2025-09-16
> OpenJDK Runtime Environment (fastdebug build 25-make-genshen-non-experimental)
> OpenJDK 64-Bit Server VM (fastdebug build 25-make-genshen-non-experimental, mixed mode)

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Update test asserting that generational mode is experimental

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/25270/files
  - new: https://git.openjdk.org/jdk/pull/25270/files/719126e6..198fb3ba

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25270&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25270&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25270.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25270/head:pull/25270

PR: https://git.openjdk.org/jdk/pull/25270