docs: clarify swc-loader default options

[chenjiahan]

Summary

This pull request updates the documentation for the tools.swc configuration, clarifying the type definition and default options.

Checklist

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

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[Copilot]

Pull Request Overview

This PR clarifies the documentation for the tools.swc configuration by providing precise TypeScript type definitions and updating the default options.

• Adds TS type definitions for ToolsSwc to clearly indicate accepted configuration types.
• Updates the default options to include experimental fields and environment settings in both English and Chinese documentation.

Reviewed Changes

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

File	Description
website/docs/zh/config/tools/swc.mdx	Introduces a clear TS type definition and documents additional default properties (experimental and env).
website/docs/en/config/tools/swc.mdx	Introduces a clear TS type definition and documents additional default properties (experimental and env).