Remove JS-based loader bridge for SWC plugin of `useExtracted` to further improve transform performance

[amannn]

Context

• SWC plugins require a compatible swc_core runtime. Old plugins only work with specific swc_core versions.
• Latest swc_core is backward-compatible, but no stable Next.js release uses it yet. Only @swc/core works reliably with backward-compatible plugins.

Current approach

• next-intl uses a JS loader bridge with @swc/core to call SWC plugins from Next.js.
• Example: next-intl depends on "@swc/core": "^1.15.2"; plugin compiled with swc_core = "47.0.3" — safe for now.
• This avoids breaking changes if Next.js upgrades swc_core and drops support for older versions.

Why no direct Next.js integration yet

• Backward-compatible swc_core exists in Next.js canary builds, but no stable release yet.
• swcPlugins config is still experimental; full backward compatibility isn’t guaranteed.
• Upgrading Next.js patch could require next-intl to upgrade swc_core, dropping support for older Next.js versions.
• Minor breaking changes for SWC plugins are expected currently

Conclusion

• The JS loader bridge is a temporary, safe solution.
• We’ll remove it once Next.js stabilizes backward-compatible SWC plugins and the swcPlugins config.

References

• fix: SWC plugin direct integration #2182
• https://blog.swc.rs/2025-11-4-wasm-backward-compatibility
• https://plugins.swc.rs/versions/range/768

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Thanks to @kdy1 for the input here!