RFR: 8139457: Array bases are aligned at HeapWord granularity [v11]

[Roman Kennke]

> See [JDK-8139457](https://bugs.openjdk.org/browse/JDK-8139457) for details.
> 
> Basically, when running with -XX:-UseCompressedClassPointers, arrays will have a gap between the length field and the first array element, because array elements will only start at word-aligned offsets. This is not necessary for smaller-than-word elements.
> 
> Also, while it is not very important now, it will become very important with Lilliput, which eliminates the Klass field and would always put the length field at offset 8, and leave a gap between offset 12 and 16.
> 
> Testing:
>  - [x] runtime/FieldLayout/ArrayBaseOffsets.java (x86_64, x86_32, aarch64, arm, riscv, s390)
>  - [x] bootcycle (x86_64, x86_32, aarch64, arm, riscv, s390)
>  - [x] tier1 (x86_64, x86_32, aarch64, riscv)
>  - [x] tier2 (x86_64, aarch64, riscv)
>  - [x] tier3 (x86_64, riscv)

Roman Kennke has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 25 commits:

 - Merge branch 'master' into JDK-8139457
 - Fix gtest for correct base offsets in 32bit builds
 - Fix cast warning
 - Revert relaxation of array length
 - Add guards to ArrayBaseOffsets test to allow running with -UseCompressedClassPointers
 - Fix another cast warning
 - Clean cast warning from size_t to int
 - Clear leading 32bits in Z array allocator
 - SA adjustments
 - Test for 32bit build
 - ... and 15 more: https://git.openjdk.org/jdk/compare/500b45e1...c278a53b

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

Changes: https://git.openjdk.org/jdk/pull/11044/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11044&range=10
  Stats: 564 lines in 32 files changed: 434 ins; 58 del; 72 mod
  Patch: https://git.openjdk.org/jdk/pull/11044.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11044/head:pull/11044

PR: https://git.openjdk.org/jdk/pull/11044