perf: optimize module resolution of compiled packages

[chenjiahan]

Summary

• Optimizes module resolution performance by using explicit index.js file paths instead of directory paths in prebundle configurations.
• Removes unused schema-utils prebundle config.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[Copilot]

Pull Request Overview

This PR optimizes module resolution performance for prebundled packages by using explicit index.js file paths instead of directory paths, and removes unused schema-utils configuration from the babel plugin.

• Replaces directory-based module paths with explicit index.js file paths in prebundle configs
• Removes unused schema-utils prebundle configuration and related code from plugin-babel
• Updates external module references to use more specific file paths for better resolution performance

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
packages/plugin-babel/prebundle.config.mjs	Removes unused schema-utils configuration and related helper functions
packages/core/prebundle.config.mjs	Updates external module paths to use explicit index.js files for improved resolution

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