RFR: Improve version check, and related doc update

[Iris Clark]

On Mon, 27 Jun 2022 21:28:53 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

> Please review a change to improve the check for old versions of `tidy`, including specifically, the default version on mac OS.
> 
> I also fixed trailing whitespace.

Marked as reviewed by iris (Reviewer).

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PR: https://git.openjdk.org/doccheck/pull/4