RFR: 8139457: Array bases are aligned at HeapWord granularity [v30]

[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 49 commits:

 - Simplify by moving gap clearing into initialize_header()
 - Merge branch 'master' into JDK-8139457
 - Rename payload_start -> payload_offset
 - Initialize gap between array-length and first element
 - Protect against overflow when dealing with TLAB::max_size()
 - Fix comment in s390
 - Rename header_size* -> base_offset* in arm
 - Merge remote-tracking branch 'origin/JDK-8139457' into JDK-8139457
 - Eliminate oopDesc::header_size()
 - Merge branch 'master' into JDK-8139457
 - ... and 39 more: https://git.openjdk.org/jdk/compare/0dca573c...75934f29

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

Changes: https://git.openjdk.org/jdk/pull/11044/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11044&range=29
  Stats: 774 lines in 48 files changed: 507 ins; 157 del; 110 mod
  Patch: https://git.openjdk.org/jdk/pull/11044.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/11044/head:pull/11044

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