feat: experimental support for ESM web applications

[chenjiahan]

Summary

Rspack has introduced ESM HMR support in recent releases. This enables Rsbuild to support the output.module: true when target is web.

As the ESM web application has not yet been fully tested, it has been marked as experimental and more test cases are planned.

Links

#6332

Checklist

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

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[Copilot]

Pull Request Overview

This PR adds experimental support for ESM web applications in Rsbuild by leveraging Rspack's recent ESM HMR support. The main purpose is to enable output.module: true for web targets while maintaining HMR functionality.

Key changes:

• Updated ESM plugin to support web targets with experimental warning and runtime chunk configuration
• Modified HTML plugin to automatically use module script loading when ESM output is enabled
• Added comprehensive HMR test coverage for ESM web applications

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/core/src/types/config.ts	Updated documentation for scriptLoading to clarify module mode behavior
packages/core/src/plugins/html.ts	Added logic to force module script loading when output.module is enabled
packages/core/src/plugins/esm.ts	Extended ESM support to web targets with experimental warning and runtime chunk fix
e2e/cases/hmr/esm/*	Added new test case for ESM HMR functionality with React components
e2e/cases/hmr/basic/index.test.ts	Minor test description and formatting improvements

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