RFR: 8139457: Array bases are aligned at HeapWord granularity

[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)

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

Commit messages:
 - More PPC fixes
 - Merge branch 'master' into JDK-8139457
 - Revert BytesPerWord/BytesPerInt change in RISCV
 - More RISCV fixes
 - Add test to verify array base offset
 - RISCV parts
 - PPC parts
 - s390 parts
 - Arm parts
 - Aarch64 parts
 - ... and 1 more: https://git.openjdk.org/jdk/compare/e81359f1...42caf4bd

Changes: https://git.openjdk.org/jdk/pull/11044/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11044&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8139457
  Stats: 246 lines in 26 files changed: 142 ins; 43 del; 61 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