RFR: 8281376: Consider polymorphic methods when looking for overrides

[Pavel Rappo]

When looking for an overridden method, javadoc treated generic method candidates differently from those nongeneric.

- The new tests fail without the fix and pass with the fix.
- JDK API Documentation built before and after are identical.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.java.net/jdk/pull/7427/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7427&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281376
  Stats: 227 lines in 5 files changed: 222 ins; 1 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7427.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7427/head:pull/7427

PR: https://git.openjdk.java.net/jdk/pull/7427