Docs: Fix broken handbook links for JavaScript build and release process

[manhphuc]

Summary

This PR fixes several broken (404) links in the Gutenberg documentation that were still pointing to removed handbook files.

The outdated internal references have been replaced with their current canonical equivalents in the Block Editor Handbook on developer.wordpress.org.

Changes

• Replaced references to the removed js-build-setup documentation with the current “Get started with wp-scripts” guide.
• Updated the Gutenberg Release Process link to point directly to the current package release and core updates documentation.
• Ensured all updated links use canonical handbook URLs to avoid redirects and future breakage.

Affected files

• docs/how-to-guides/platform/README.md
• docs/how-to-guides/data-basics/1-data-basics-setup.md
• docs/how-to-guides/block-tutorial/README.md
• docs/contributors/documentation/README.md
• docs/contributors/code/managing-packages.md

These changes improve the accuracy and usability of the documentation without altering any technical content.

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Co-authored-by: manhphuc <manhphucofficial@git.wordpress.org>

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[youknowriad]

Thanks @manhphuc, and sorry this sat so long. These links were all fixed in the meantime — WordPress/gutenberg#81232 handled the JavaScript build setup references and the release link was updated separately, both pointing at repo-relative paths so they resolve on GitHub, in the handbook and on npm. There are no references left to the removed files, so I'm closing this as superseded. Thanks for spotting them!