RFR: 8289740: Add verification testing during all concurrent phases in G1 [v3]

[Thomas Schatzl]

> Hi all,
> 
>   can I have reviews for this change that adds a test that causes GCs that do lots of verification in all phases of the concurrent cycle to make sure that verification is working after changes.
> 
> Testing: test case, gha
> 
> Thanks,
>   Thomas

Thomas Schatzl 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 four additional commits since the last revision:

 - Merge branch 'master' into pull/9377
 - Add test
 - Add test
 - Initial change, adding new concurrent cycle breakpoints

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/9377/files
  - new: https://git.openjdk.org/jdk/pull/9377/files/eed786bd..1b82991a

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9377&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9377&range=01-02

  Stats: 7577 lines in 195 files changed: 4096 ins; 1963 del; 1518 mod
  Patch: https://git.openjdk.org/jdk/pull/9377.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9377/head:pull/9377

PR: https://git.openjdk.org/jdk/pull/9377