RFR: 8329994: Zap alignment padding bits for ArrayOops in non-release builds [v2]

[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 incrementally with one additional commit since the last revision:

  Rename to mem_zap_start_padding

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/18714/files
  - new: https://git.openjdk.org/jdk/pull/18714/files/13d52eff..1ffc1e5b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18714&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18714&range=00-01

  Stats: 4 lines in 3 files changed: 0 ins; 0 del; 4 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