[lworld] RFR: 8251966: [lworld] TestArrays.java fails with -XX:+ExpandSubTypeCheckAtParseTime

[Tobias Hartmann]

[JDK-8251442](https://bugs.openjdk.java.net/browse/JDK-8251442) added SubTypeCheckNode optimizations that make sure that the control path consistently dies with the data path. These need to be implemented in `CmpPNode::sub` as well which requires `TypeKlassPtr` to keep track of not null-free/flat properties for array klasses.

Thanks,
Tobias

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Commit messages:
 - 8251966: [lworld] TestArrays.java fails with -XX:+ExpandSubTypeCheckAtParseTime

Changes: https://git.openjdk.java.net/valhalla/pull/281/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=281&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8251966
  Stats: 71 lines in 6 files changed: 30 ins; 3 del; 38 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/281.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/281/head:pull/281

PR: https://git.openjdk.java.net/valhalla/pull/281