RFR: 8336043: Add quality of implementation discussion to Object.{equals, toString, hashCode} [v5]

[Joe Darcy]

> First pass at adding some quality of implementation discussions around the overridable methods of Object.

Joe Darcy has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - Fix typo found in code review.
 - Merge branch 'master' into JDK-8336043
 - Merge branch 'master' into JDK-8336043
 - Respond to review feedback.
 - Merge branch 'master' into JDK-8336043
 - Appease jcheck.
 - JDK-8336043: Add quality of implementation discussion to Object.{equals, toString, hashCode}

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20128/files
  - new: https://git.openjdk.org/jdk/pull/20128/files/80cabee0..840ee4f2

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20128&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20128&range=03-04

  Stats: 9191 lines in 323 files changed: 4525 ins; 3108 del; 1558 mod
  Patch: https://git.openjdk.org/jdk/pull/20128.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20128/head:pull/20128

PR: https://git.openjdk.org/jdk/pull/20128