RFR: 8303516: HFAs with nested structs/unions/arrays not handled correctly on AArch64

[Jorn Vernee]

Port of: https://github.com/openjdk/panama-foreign/pull/780 Which adds tests for nested structs/unions/arrays, and fixes an issue with nested HFAs on AArch64.

This PR also includes https://github.com/openjdk/panama-foreign/pull/765 which is required for the fix to apply cleanly.

Moving these change sets into the mainline now seems useful for the currently ongoing porting effort on PPC, as well as taking a load off of the JEP PR review which will come later.

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Commit messages:
 - disable test on x86
 - update copyright years
 - 8300294: Add tests for by-value unions and structs with nested fixed-length arrays
 - 8299911: Refactor struct handling in AArch64 CallArranger

Changes: https://git.openjdk.org/jdk/pull/12831/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12831&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303516
  Stats: 1046 lines in 8 files changed: 786 ins; 174 del; 86 mod
  Patch: https://git.openjdk.org/jdk/pull/12831.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12831/head:pull/12831

PR: https://git.openjdk.org/jdk/pull/12831