[lworld] RFR: 8350515: [lworld] CheckedType replaced by NullRestricted

[Roger Riggs]

The support for CheckedType is replaced by an explicit attribute for NullRestricted. VarHandles for fields and arrays are updated to match.

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Commit messages:
 - 8350515: [lworld] CheckedType replaced by NullRestricted

Changes: https://git.openjdk.org/valhalla/pull/1434/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1434&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350515
  Stats: 301 lines in 9 files changed: 9 ins; 227 del; 65 mod
  Patch: https://git.openjdk.org/valhalla/pull/1434.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1434/head:pull/1434

PR: https://git.openjdk.org/valhalla/pull/1434