RFR: 7904086: Fix docs that JUnit tests need no `@build` for `@library` contents

[duke]

On Thu, 25 Sep 2025 09:23:33 GMT, Volkan Yazici <vyazici at openjdk.org> wrote:

> If a library directory is used by a directory of TestNG **or JUnit** tests, all the classes in a library directory will be automatically compiled by means of implicit `@build` tags. Amend the docs accordingly.

@vy 
Your change (at version df529856f52d5edde2c6a1ab4cf55ee630e31ddb) is now ready to be sponsored by a Committer.

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PR Comment: https://git.openjdk.org/jtreg/pull/292#issuecomment-3333351981