RFR: 8301988: VerifyLiveClosure::verify_liveness asserts on bad pointers outside heap

[Thomas Schatzl]

Hi all,

  can I have reviews for this change to liveness verification that fixes some unwanted asserts because

 - it uses decode_not_null which will assert if the given oop address is not in the heap, making the remainder of the verification useless in that case
- if the referenced object is not in the heap, we try to get its heap region too when printing, which also fails some assertions
- in the innermost if lots of code is duplicated in both cases 

The first two issues are really annoying (there is another one when the `Klass` is garbage when calling `is_obj_dead_cond`, but I'll fix that separately).

Testing: local compilation/testing, gha

Thanks,
  Thomas

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Commit messages:
 - initial version

Changes: https://git.openjdk.org/jdk/pull/12456/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12456&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301988
  Stats: 29 lines in 3 files changed: 13 ins; 12 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/12456.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12456/head:pull/12456

PR: https://git.openjdk.org/jdk/pull/12456