[esnext] Fix various callsites to use is_resumable, not is_generator

test/mjsunit/harmony/async-await-basic.js

Index: test/mjsunit/harmony/async-await-basic.js
diff --git a/test/mjsunit/harmony/async-await-basic.js b/test/mjsunit/harmony/async-await-basic.js
index d0888eaf33ffca6869152e1f4444188a55f61b7f..40a2605177aee33d97c57f72a6cc31907a920ee5 100644
--- a/test/mjsunit/harmony/async-await-basic.js
+++ b/test/mjsunit/harmony/async-await-basic.js
@@ -345,3 +345,6 @@ assertEquals("async x => { return x }", (async x => { return x }).toString());
 class AsyncMethod { async foo() { } }
 assertEquals("async foo() { }", Function.prototype.toString.call(AsyncMethod.prototype.foo));
 assertEquals("async foo() { }", Function.prototype.toString.call({async foo() { }}.foo));
+
+// Async functions are not constructible
+assertThrows(() => class extends (async function() {}) {}, TypeError);