RFR: 8303334: Further improve liveness/remembered set verification for G1 [v2]

[Thomas Schatzl]

> Hi all,
> 
>   can I have reviews for this additional refactoring of the liveness/remembered set code? After having pushed [JDK-8302760](https://bugs.openjdk.org/browse/JDK-8302760), @albertnetymk suggested some more changes to improve readability mainly in `G1VerifyLiveAndRememberedSetsClosure` to make program flow more obvious.
> I.e. it separates the steps of detecting and reporting the failures explicitly.
> Everything else follows that.
> 
> Testing: local compilation, gha, testing on some failure code
> 
> Thanks,
>   Thomas

Thomas Schatzl has updated the pull request incrementally with one additional commit since the last revision:

  class -> struct

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12807/files
  - new: https://git.openjdk.org/jdk/pull/12807/files/303ad64c..cd41d844

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12807&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12807&range=00-01

  Stats: 6 lines in 1 file changed: 0 ins; 3 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/12807.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12807/head:pull/12807

PR: https://git.openjdk.org/jdk/pull/12807