RFR: 8253566: clazz.isAssignableFrom will return false for interface implementors

[Roland Westrelin]

The code pattern in the test case is optimized as a trichotomy which
is wrong given SubTypeCheckNode is a special kind of CmpNode that's
not commutative.

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Commit messages:
 - comment
 - test
 - trichotomy opt should not be applied to subtype check

Changes: https://git.openjdk.java.net/jdk/pull/422/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=422&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253566
  Stats: 71 lines in 2 files changed: 70 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/422.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/422/head:pull/422

PR: https://git.openjdk.java.net/jdk/pull/422