RFR: 8331920: ubsan: g1CardSetContainers.inline.hpp:266:5: runtime error: index 2 out of bounds for type 'G1CardSetHowl::ContainerPtr [2]' reported

[Ivan Walulya]

Hi all,

Please review this change to improve access to G1CardSetContainer VLA elements. Instead of  straightforward indexing, we obscure access through a base pointer and offsets to reduce the possibility of UB. 

Testing: Tier 1-3
              - Local testing on Mac with `--enable-ubsan`.

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Commit messages:
 - add comments
 - Merge remote-tracking branch 'upstream/master' into JDK-8331920-ubsan
 - Merge branch 'master' into JDK-8331920-ubsan
 - obscure access

Changes: https://git.openjdk.org/jdk/pull/19300/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19300&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331920
  Stats: 37 lines in 3 files changed: 25 ins; 2 del; 10 mod
  Patch: https://git.openjdk.org/jdk/pull/19300.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19300/head:pull/19300

PR: https://git.openjdk.org/jdk/pull/19300