build(core): enable advanced ESM

[chenjiahan]

Summary

Enable Rslib's advanced ESM features for all ESM builds of @rsbuild/core.

Before

File (esm_index)         Size
dist/0~range-parser.js   2.4 kB
dist/0~open.js           18.3 kB
dist/index.js            495.2 kB

                Total:   515.9 kB


File (esm_loaders)            Size
dist/ignoreCssLoader.mjs      0.19 kB
dist/transformLoader.mjs      2.1 kB
dist/transformRawLoader.mjs   2.1 kB

                     Total:   4.5 kB

After

File (esm_index)         Size
dist/0~range-parser.js   2.3 kB
dist/rslib-runtime.js    2.3 kB
dist/0~open.js           14.9 kB
dist/index.js            489.7 kB

                Total:   509.2 kB


File (esm_loaders)            Size
dist/ignoreCssLoader.mjs      0.13 kB
dist/223.mjs                  0.55 kB
dist/transformLoader.mjs      1.6 kB
dist/transformRawLoader.mjs   1.7 kB

                     Total:   4.0 kB

Related Links

• https://rspack.rs/blog/announcing-1-6#improved-esm-output

Checklist

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

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[Copilot]

Pull Request Overview

This PR enables the advancedEsm experimental feature for all ESM format builds in the core package. This configuration is applied to improve ESM output handling.

• Adds experiments.advancedEsm: true to all ESM format library configurations
• Ensures consistent configuration across esm_index, esm_loaders, and esm_client builds
• Leaves CJS builds unchanged as the feature is ESM-specific

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