[lworld] RFR: 8345995: [lworld] Flat arrays need to be redesigned to support new flat layouts

[Frederic Parain]

Here's a redesign of flat arrays to support multiple flat layouts (NON_ATOMIC_FLAT, ATOMIC_FLAT, NULLABLE_ATOMIC_FLAT). The patch contains a lot of cleanup and simplification of the flat arrays access code.

This patch has been tested in interpreted mode only on both x86_64 and aarch64.

Unfortunately, it currently triggers a number of failures when run with JITs enabled. After a discussion with Tobias, this PR will probably not be integrated until a patch for the JITs is available.

Regards,

Fred

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Commit messages:
 - CDS fixes and various cleanup
 - Merge remote-tracking branch 'upstream/lworld' into array_ext_hdr
 - More flat arrays work and code cleanup

Changes: https://git.openjdk.org/valhalla/pull/1315/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1315&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8345995
  Stats: 1556 lines in 62 files changed: 933 ins; 281 del; 342 mod
  Patch: https://git.openjdk.org/valhalla/pull/1315.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1315/head:pull/1315

PR: https://git.openjdk.org/valhalla/pull/1315