change minimal sample's fetch helper to artificially delay

the delay is longer that the threadpool worker's semaphore timeout, in
order to validate that the worker stays alive while there are
unsettled promises

Author: lambdageek

src/mono/sample/wasm/browser-threads-minimal/fetchhelper.js

@@ -1,4 +1,11 @@
 
-export function responseText(response) /* Promise<string> */ {
-  return response.text();
+function delay(timeoutMs) {
+    return new Promise(resolve => setTimeout(resolve, timeoutMs));
+}
+
+export async function responseText(response) /* Promise<string> */ {
+  console.log("artificially waiting for response for 25 seconds");
+  await delay(25000);
+  console.log("artificial waiting done");
+  return await response.text();
 }