RFR: 8307181: MemoryLayout.structLayout uses undocumented strict alignment constraints [v2]

[Maurizio Cimadamore]

> 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.

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Update src/java.base/share/classes/java/lang/foreign/MemoryLayout.java
  
  Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13770/files
  - new: https://git.openjdk.org/jdk/pull/13770/files/592a3db6..3be3a685

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13770&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13770&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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