RFR: 8290918: Initial nroff manpage generation for JDK 21

[David Holmes]

On Mon, 23 Jan 2023 23:24:06 GMT, Lance Andersen <lancea at openjdk.org> wrote:

>> Please review this simple update to the manpage to set the version to 21-ea.
>> 
>> This change also corrects a typo in javac.1 that was manually introduced by JDK-8300591
>> 
>> Thanks.
>
> Marked as reviewed by lancea (Reviewer).

Thanks for the review @LanceAndersen

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PR: https://git.openjdk.org/jdk/pull/12154