RFR: 8338780: GenShen: Fix up some comments [v2]

[Y. Srinivas Ramakrishna]

> In https://github.com/openjdk/jdk/pull/20395 Aleksey provided some suggestions for improving various comments. This ticket gathers together several of those changes.
> 
> **Testing:** 
> - [x] GHA
> - [x] SPECjbb w/GenShen
> - [x] jtreg:tier1
> - [x] jtreg:hotspot_gc (one test fails with OOM in master as well as current branch; will investigate that separately)
> - [ ] Codepipeline testing (in progress)

Y. Srinivas Ramakrishna 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 six additional commits since the last revision:

 - Merge branch 'master' into review_changes_2
 - Cleanup and get ready for testing & review.
 - Sharpen assert for testing. Need more changes after this. Don't review
   yet.
 - Testing only: do not review this change.
 - Merge branch 'master' into review_changes_2
 - JDK-8338780 GenShen: Fix up some comments

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

Changes:
  - all: https://git.openjdk.org/shenandoah/pull/484/files
  - new: https://git.openjdk.org/shenandoah/pull/484/files/2e889682..9e994326

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=484&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=484&range=00-01

  Stats: 47 lines in 4 files changed: 1 ins; 34 del; 12 mod
  Patch: https://git.openjdk.org/shenandoah/pull/484.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/484/head:pull/484

PR: https://git.openjdk.org/shenandoah/pull/484