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

[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

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

Commit messages:
 - Remove max failure guard in main routine
 - Limit per-thread failures to G1MaxNumVerifyFailures
 - albert-idea

Changes: https://git.openjdk.org/jdk/pull/12807/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12807&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303334
  Stats: 134 lines in 1 file changed: 69 ins; 25 del; 40 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