RFR: 8325870: Zap end padding bits for ArrayOops in non-release builds [v2]

[Axel Boldt-Christmas]

> Make `ObjArrayAllocator` zap the end padding bits in not PRODUCT builds.
> 
> Issues like [JDK-8325074](https://bugs.openjdk.org/browse/JDK-8325074) / #17863 would then reproduce deterministically. Avoid future regressions.
> 
> Guarded `Copy::fill_to_bytes`, it was not clear if or how it handles `count == 0`. Given that almost all dispatch to memset, the `count == 0` would probably be alright, but as `obj_end - padding_in_bytes` may point beyond an object and thus outside the heap it seems prudent to guard it (I believe memset requires a valid pointer).

Axel Boldt-Christmas has updated the pull request incrementally with three additional commits since the last revision:

 - Update copyright years
 - Use *_end pointers and add assert
 - Rename heapPaddingByte to heapPaddingByteVal

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/17864/files
  - new: https://git.openjdk.org/jdk/pull/17864/files/9504304e..eec91e9e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17864&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17864&range=00-01

  Stats: 24 lines in 4 files changed: 2 ins; 0 del; 22 mod
  Patch: https://git.openjdk.org/jdk/pull/17864.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17864/head:pull/17864

PR: https://git.openjdk.org/jdk/pull/17864