[feature request] detect and defer to native implementations of `fetch` global

[DerekNonGeneric]

Detect and defer to native implementations

For features that have reached the tipping point, where the polyfill registers the same name as the native feature, include code to detect a native implementation, and if one exists, defer to it. Where a native feature exists but is incomplete or buggy, consider using as much of it as possible and correcting only the deficiencies.

— https://www.w3.org/2001/tag/doc/polyfills/#detect-and-defer-to-native-implementations

Additionally, consider replacing node-fetch dependency with undici for behavior guarantees.

[DerekNonGeneric]

See w3ctag/design-principles#357 for further guidance on this exact situation.