RFR: 8302206: Factor out duplicate G1VerificationClosure [v4]

[Thomas Schatzl]

> Hi all,
> 
>   can I have reviews for this cleanup that merges `G1VerifyLiveClosure` from `g1FullGCMarker.cpp` and `VerifyLiveClosure` from `heapRegion.cpp` into a single one as they are virtually identical.
> 
> There is probably one change that needs some discussion, and that is about changing the type and meaning of `G1MaxVerifyFailures`: after changing the type of `G1VerificationClosure::_num_failures` to uint, the given comparison does not work any more due to differing types.
> However the change of the default value to `0` meaning "show all messages" does not seem too bad: even before this change, a value of `0` at least showed one failure as this check (now it shows all messages) is located after the error printing in the closures.
> It's a develop flag too, so instead of casting around I chose to simply change the meaning.
> 
> Testing: gha
> 
> Thanks,
>   Thomas

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

  Minor removal of unnecessary code

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/12511/files
  - new: https://git.openjdk.org/jdk/pull/12511/files/b1dc2be1..e6bfc0cf

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12511&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12511&range=02-03

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/12511.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12511/head:pull/12511

PR: https://git.openjdk.org/jdk/pull/12511