RFR: JDK-8310453: Update javadoc of java.lang.Object

[Joe Darcy]

I had occasion to read over the javadoc sources in java.lang.Object recently and noticed a few items that could be updated.

There are some new or expanded API notes referring to methods in java.util.Objects. I added these references as apiNote items rather than, say, `@see` tags since  `@see` tag changes would propagate into classes that overrode the methods in questions.

Changing toString to use an inline `@return` tag has the consequence of omitting a trailing period, "." in the "Returns" section of its javadoc. This also omits  a trailing period in subclasses that use the `@return` statement of Object.toString in their own toString method. Likewise for hashCode.

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Commit messages:
 - JDK-8310453: Update javadoc of java.lang.Object

Changes: https://git.openjdk.org/jdk/pull/14567/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=14567&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8310453
  Stats: 25 lines in 1 file changed: 11 ins; 1 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/14567.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14567/head:pull/14567

PR: https://git.openjdk.org/jdk/pull/14567