RFR: 8139457: Array bases are aligned at HeapWord granularity [v37]

[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 57 commits:

 - Merge branch 'master' into JDK-8139457
 - Correctly handle oop array element aligment in 32bit builds; move method from Universe to Array
 - Require uncompressed oops to be 8-byte-aligned
 - Corresponding XGC fixes
 - Merge branch 'master' into JDK-8139457
 - Fix calls to removed instanceOopDesc::header_size()
 - Add cast
 - Simplify aarch64 code
 - Simplify by moving gap clearing into initialize_header()
 - Merge branch 'master' into JDK-8139457
 - ... and 47 more: https://git.openjdk.org/jdk/compare/ba974d5c...1d3db84e

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Changes: https://git.openjdk.org/jdk/pull/11044/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11044&range=36
  Stats: 806 lines in 50 files changed: 526 ins; 164 del; 116 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