RFR: JDK-8302019: Clarify Elements.overrides

[Joe Darcy]

Explicitly discuss and test handling of an interface declaring methods that "override" public methods on java.lang.Object.

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Commit messages:
 - Appease jcheck.
 - JDK-8302019: Clarify Elements.overrides

Changes: https://git.openjdk.org/jdk/pull/17564/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17564&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8302019
  Stats: 129 lines in 2 files changed: 129 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/17564.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17564/head:pull/17564

PR: https://git.openjdk.org/jdk/pull/17564