Always use node-fetch and stop polyfilling

Due to a bug in undici (nodejs/undici#1776)
that is affecting many versions of Node and Next.js,
we want a workaround to ensure our users don't see this.

Therefore, we're forking isomorphic-unfetch to always use node-fetch
on Node to avoid falling back to global.fetch (undici).

Also, isomorphic-unfetch was polyfilling, which we want to avoid.

packages/isomorphic-unfetch/index.js

@@ -1,10 +1,8 @@
 function r(m) {
 	return (m && m.default) || m;
 }
-module.exports = global.fetch =
-	global.fetch ||
-	(typeof process == "undefined"
-		? r(require("unfetch"))
+module.exports = (typeof process == "undefined"
+		? global.fetch || r(require("unfetch"))
 		: function (url, opts) {
 				if (typeof url === "string" || url instanceof URL) {
 					url = String(url).replace(/^\/\//g, "https://");

packages/isomorphic-unfetch/index.mjs

@@ -1,10 +1,8 @@
 function r(m) {
 	return (m && m.default) || m;
 }
-export default global.fetch =
-	global.fetch ||
-	(typeof process == "undefined"
-		? function (url, opts) {
+export default fetch = (typeof process == "undefined"
+		? global.fetch || function (url, opts) {
 				return import("unfetch").then((m) => r(m)(url, opts));
 		  }
 		: function (url, opts) {

test/isomorphic.test.js

@@ -87,7 +87,7 @@ describe("isomorphic-unfetch", () => {
 	});
 
 	describe('"main" entry in NodeJS', () => {
-		it("should resolve to fetch when window.fetch exists", async () => {
+		it("should resolve to node-fetch (changed from upstream for Plasmic) when window.fetch exists", async () => {
 			let sandbox = {
 				process: {},
 				global: { fetch },
@@ -117,7 +117,7 @@ describe("isomorphic-unfetch", () => {
 
 			const ns = mod.namespace;
 
-			expect(await ns.default("/")).toBe("this is fetch");
+			expect(await ns.default("/")).toBe("this is node-fetch");
 		});
 
 		it("should resolve to node-fetch when window.fetch does not exist", async () => {