RFR: 8329858: G1: Make G1VerifyLiveAndRemSetClosure stateless

[Stefan Karlsson]

In [JDK-8329570](https://bugs.openjdk.org/browse/JDK-8329570): 'G1: Excessive is_obj_dead_cond calls in verification' we moved the verification of the containing object so that it was done only once. We left the repeated null-check because of concerns that moving it would introduce the risk that someone in the future would miss calling `set_containing_obj` or calling it with a null object.

I propose that we restructure the code to make the closure's state const and remove the set_containing_obj function so that we can feel confident that we don't hit such a bug in the future.

The patch also combines the failures from verification of the oops with failures from checking the containing objects. I had a version that kept these two separate, but I don't see why we would want that. Tell me if you'd want me to reintroduce this separation.

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Commit messages:
 - 8329858: G1: Make G1VerifyLiveAndRemSetClosure stateless

Changes: https://git.openjdk.org/jdk/pull/18677/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18677&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8329858
  Stats: 55 lines in 1 file changed: 21 ins; 9 del; 25 mod
  Patch: https://git.openjdk.org/jdk/pull/18677.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18677/head:pull/18677

PR: https://git.openjdk.org/jdk/pull/18677