[jdk18] RFR: 8278897: Alignment of heap segments is not enforced correctly

[Maurizio Cimadamore]

This PR fixes an issue with alignment constraints not being enforced correctly on on-heap segments dereference/copy operations. Alignment of on-heap segments cannot be computed exactly, as alignment of elements in arrays is, ultimately a VM implementation detail. Because of this, alignment checks on heap segments can fail or pass depending on the platform being used.

For more details about the problem and the solution please refer to:
https://mail.openjdk.java.net/pipermail/panama-dev/2021-November/015852.html

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Commit messages:
 - Initial push

Changes: https://git.openjdk.java.net/jdk18/pull/37/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18&pr=37&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278897
  Stats: 600 lines in 20 files changed: 566 ins; 0 del; 34 mod
  Patch: https://git.openjdk.java.net/jdk18/pull/37.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18 pull/37/head:pull/37

PR: https://git.openjdk.java.net/jdk18/pull/37