[lworld+vector] RFR: Merge lworld

[Jatin Bhateja]

Merge latest lworld changes into lworld+vector branch.

Validation Status with this patch:-

-  All the tests under test/hotspot/jtreg/compiler/valhalla/inlinetypes are now passing at various AVX levels.
- No new Vector API jtreg test failure seen.

Best Regards,
Jatin

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Commit messages:
 - jcheck failure resolution, whitespace removal
 - Remove multifield related special handling from C1
 - Merge branch 'lworld' of http://github.com/openjdk/valhalla into merge_lworld
 - 8315935: [lworld] Apply flat renaming to C2 code
 - 8311219: [lworld] VM option "InlineFieldMaxFlatSize" cannot work well
 - 8313667: [lworld] XBarrierSetC2::clone_at_expansion() uses wrong array copy stub for cloning flat primitive type arrays
 - 8315412: [lworld] Preparing code for lw5
 - 8315272: [lworld] Replacing NULL with nullptr in aarch64 code

The webrevs contain the adjustments done while merging with regards to each parent branch:
 - lworld+vector: https://webrevs.openjdk.org/?repo=valhalla&pr=929&range=00.0
 - lworld: https://webrevs.openjdk.org/?repo=valhalla&pr=929&range=00.1

Changes: https://git.openjdk.org/valhalla/pull/929/files
  Stats: 1312 lines in 110 files changed: 320 ins; 119 del; 873 mod
  Patch: https://git.openjdk.org/valhalla/pull/929.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/929/head:pull/929

PR: https://git.openjdk.org/valhalla/pull/929