fix(create-rslib): use js config for esm templates

[Timeless0911]

Summary

This PR updates JavaScript create-rslib templates that already declare "type": "module" to use rslib.config.js instead of rslib.config.mjs, since ESM syntax is handled by the package type. It also updates the create-rslib test helper to validate the new config filename for JS React templates.

Checklist

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

[Copilot]

Pull request overview

This PR renames generated JavaScript ESM template configs from .mjs to .js where "type": "module" already enables ESM syntax.

Changes:

• Adds rslib.config.js files for React JS, React Compiler JS, and Node JS templates.
• Updates the React template test helper to expect rslib.config.js for JS React projects.

Reviewed changes

Copilot reviewed 1 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/create-rslib/test/helper.ts	Updates JS React config filename assertion.
packages/create-rslib/template-react-js/rslib.config.js	Adds React JS Rslib config using ESM syntax.
packages/create-rslib/template-react-compiler/react-js/rslib.config.js	Adds React Compiler JS Rslib config.
packages/create-rslib/template-node-esm-js/rslib.config.js	Adds Node ESM JS Rslib config.
packages/create-rslib/template-node-dual-js/rslib.config.js	Adds Node dual-format JS Rslib config.