Slightly improve experimental.mdxRs error message with Webpack (#68356)

This is of course still not great. Is there a way/will to have
codeframes similar to vercel/turborepo#8879 when
using Webpack?

Before:
```
Error: page.mdx:Error: Message { place: Some(Point(7:1 (87))), reason: "Unexpected end of file in expression, expected a corresponding closing brace for `{`", rule_id: "unexpected-eof", source: "markdown-rs" }

Import trace for requested module:
./app/blog/hello-world/page.mdx
 ⨯ ./app/blog/hello-world/page.mdx
```

After:
```
Error: page.mdx:Error: 7:1: Unexpected end of file in expression, expected a corresponding closing brace for `{` (markdown-rs:unexpected-eof)

Import trace for requested module:
./app/blog/hello-world/page.mdx
 ⨯ ./app/blog/hello-world/page.mdx
```

Author: mischnic

crates/napi/src/mdx.rs

@@ -14,7 +14,7 @@ impl Task for MdxCompileTask {
         let options: Options = serde_json::from_slice(&self.option)?;
 
         compile(&self.input, &options)
-            .map_err(|err| napi::Error::new(Status::GenericFailure, format!("{:?}", err)))
+            .map_err(|err| napi::Error::new(Status::GenericFailure, err.to_string()))
     }
 
     fn resolve(&mut self, _env: Env, output: Self::Output) -> napi::Result<Self::JsValue> {