formData.keys, .entries is not a function

[tranzium]

Bug Description

When using request.formData() and obtaining a FormData object, both the "entries" and "keys" methods are not found.

Reproducible By

import { FromData } from "undici";
const formData = new FormData();
formData.append("key", "value");
console.log("entries" in formData); // false
console.log("keys" in formData); // false

Expected Behavior

console.log("entries" in formData); // true
console.log("keys" in formData); // true

Environment

miniflare --version // 2.0.0-next.3

Additional context

cloudflare/miniflare#91