RFR: 8351077: Shenandoah: Update comments in ShenandoahConcurrentGC::op_reset_after_collect [v2]

[Xiaolong Peng]

> This is a trivial PR to update the code comments in ShenandoahConcurrentGC::op_reset_after_collect.
> 
> After doing more test and analysis, we have a better understanding why reset bitmap of young gen after concurrent cycle may cause crash if there is pending old GC cycle to execute: When there is soft reference in old gen, but the referent is in young, reseting bitmap of young will cause wrong state of the soft reference, which may lead to expected cashes.

Xiaolong Peng has updated the pull request incrementally with one additional commit since the last revision:

  Update code comments as suggested in PR

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/23872/files
  - new: https://git.openjdk.org/jdk/pull/23872/files/3764bf7d..d760471e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=23872&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23872&range=00-01

  Stats: 3 lines in 1 file changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/23872.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23872/head:pull/23872

PR: https://git.openjdk.org/jdk/pull/23872