[lworld] RFR: 8265118: [lworld] C1 should optimize inline type checkcasts

[Tobias Hartmann]

C1's `Canonicalizer::do_CheckCast` should optimize casts to inline klasses when types are known. 

I've added an additional test for null casts and fixed (unrelated) `TestFieldTypeMismatch.java` which was part of the wrong package.

Thanks,
Tobias

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Commit messages:
 - 8265118: [lworld] C1 should optimize inline type checkcasts

Changes: https://git.openjdk.java.net/valhalla/pull/383/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=383&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8265118
  Stats: 32 lines in 5 files changed: 18 ins; 2 del; 12 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/383.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/383/head:pull/383

PR: https://git.openjdk.java.net/valhalla/pull/383