RFR: 8336043: Add quality of implementation discussion to Object.{equals, toString, hashCode} [v2]

[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 three additional commits since the last revision:

 - 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/150713fe..81245907

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20128&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20128&range=00-01

  Stats: 11244 lines in 484 files changed: 7156 ins; 2247 del; 1841 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