RFR: 8301721: lookup.findSpecial fails on Object method call from interface

[Mandy Chung]

Lookup.findSpecial fails on Object method call from an interface because of a bug in the implementation calling `Class::getSuperclass` on an interface which has no superclass.   The implementation should only search the method from its superclass only if it's a class.   This patch is trivial and skip the superclass search if it's an interface.

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Commit messages:
 - clean up test
 - Merge branch 'master' of https://github.com/openjdk/jdk into JDK-8301721
 - 8301721: lookup.findSpecial fails on Object method call from interface

Changes: https://git.openjdk.org/jdk/pull/14319/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14319&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8301721
  Stats: 80 lines in 2 files changed: 79 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/14319.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14319/head:pull/14319

PR: https://git.openjdk.org/jdk/pull/14319