RFR: JDK-8266536: Provide a variant of os::iso8601_time which works with arbitrary timestamps [v4]

[Thomas Stuefe]

On Fri, 7 May 2021 06:49:14 GMT, Yasumasa Suenaga <ysuenaga at openjdk.org> wrote:

> Looks good!
> I think `needed_buffer` in `os::iso8601_time()` is no longer needed, but it's ok if it is left.

Thanks Yasumasa! I changed the code a bit and removed needed_buffer.

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PR: https://git.openjdk.java.net/jdk/pull/3869