RFR: 8307181: MemoryLayout.structLayout uses undocumented strict alignment constraints

Wed May 3 08:39:23 UTC 2023

This patch adds documentation for the behavior of the `MemoryLayout::structLayout` factory.

This factory throws an `IllegalArgumentException` if one of the member layouts passed to it occurs at an offset within the struct that is not aligned.

As part of this patch, I've also added some api notes on how to use this factory when unaligned elements are present.

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Commit messages:
 - Initial push

Changes: https://git.openjdk.org/jdk/pull/13770/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13770&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307181
  Stats: 22 lines in 1 file changed: 22 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13770.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13770/head:pull/13770

PR: https://git.openjdk.org/jdk/pull/13770