RFR: 8276700: Improve java.lang.ref.Cleaner javadocs [v4]

[Roger Riggs]

On Wed, 10 Nov 2021 11:59:16 GMT, Hendrik Schreiber <hschreiber at openjdk.org> wrote:

>> Trivial improvement.
>> 
>> Explicitly show how to create a `Cleaner` instance using `Cleaner.create()`.
>> Repeat (again) in the code example that the `State` `Runnable `should be implemented as static class and not reference the instance to be cleaned, to make the point even more clear to those people who never read the javadoc *prose*.
>> 
>> I have signed the OCA a while back as [hschreiber](https://openjdk.java.net/census#hschreiber).
>
> Hendrik Schreiber has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Added extra info to Cleaner comment.

LGTM

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Marked as reviewed by rriggs (Reviewer).

PR: https://git.openjdk.java.net/jdk/pull/6076