RFR: 8329994: Zap alignment padding bits for ArrayOops in non-release builds [v3]

[Axel Boldt-Christmas]

> In a similar vein to [JDK-8325870](https://bugs.openjdk.org/browse/JDK-8325870). Zap the any alignment padding that may exist between the header and the payload.
> 
> Currently this padding only occurs when disabling `UseCompressedClassPointers`. But becomes more relevant with [JDK-8294992](https://bugs.openjdk.org/browse/JDK-8294992).

Axel Boldt-Christmas 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 three additional commits since the last revision:

 - Merge branch 'openjdk:master' into JDK-8329994
 - Rename to mem_zap_start_padding
 - 8329994: Zap alignment padding bits for ArrayOops in non-release builds

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18714/files
  - new: https://git.openjdk.org/jdk/pull/18714/files/1ffc1e5b..d47780d7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18714&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18714&range=01-02

  Stats: 264967 lines in 5198 files changed: 157091 ins; 79673 del; 28203 mod
  Patch: https://git.openjdk.org/jdk/pull/18714.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18714/head:pull/18714

PR: https://git.openjdk.org/jdk/pull/18714