[lworld] RFR: 8341767: [lworld] JIT support for nullable, atomic, flat arrays

[Tobias Hartmann]

C1 and C2 support for the new nullable, atomic, flat arrays (see [JDK-8345995](https://bugs.openjdk.org/browse/JDK-8345995) for runtime). Follow-up work will be done with [JDK-8350865](https://bugs.openjdk.org/browse/JDK-8350865) and is marked with `// TODO 8350865` in the code. Most complexity is in C2 due to the additional runtime checks and the conversion between scalarized values and atomic accesses.

Thanks,
Tobias

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Commit messages:
 - More refactoring
 - Merge branch 'JDK-8341767' of github.com:TobiHartmann/valhalla into JDK-8341767
 - Trailing whitespace
 - Merge branch 'lworld' into JDK-8341767
 - Runtime check for atomicity
 - More refactoring
 - Fixed last layout test case
 - Arraycopy fixes
 - More fixes, refactoring
 - Merge branch 'lworld' into JDK-8341767
 - ... and 21 more: https://git.openjdk.org/valhalla/compare/b37178a0...f1295977

Changes: https://git.openjdk.org/valhalla/pull/1397/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1397&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8341767
  Stats: 2500 lines in 63 files changed: 1874 ins; 335 del; 291 mod
  Patch: https://git.openjdk.org/valhalla/pull/1397.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1397/head:pull/1397

PR: https://git.openjdk.org/valhalla/pull/1397