chore: files instead of .npmignore for better readability

[haoqunjiang]

Description

See discussions at #3656 (comment)

This PR achieves the same functionality as #3656, but uses fewer negated glob patterns.

Additional context

Output of npm pack before and after this PR:
https://www.diffchecker.com/8e5xXXjV

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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• Read the Contributing Guidelines.
• Read the Pull Request Guidelines and follow the Commit Convention.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.