[explicit-resource-management] Fix async disposal

This CL fixes the async disposal from sync methods that return
a promise. The result of calling `symbol.dispose` should
not be used to resolve the outer promise.

Bug: 42203814
Change-Id: I4c4573035b74b06ad78e2810e3f132301954c048
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/6291492
Reviewed-by: Shu-yu Guo <syg@chromium.org>
Commit-Queue: Rezvan Mahdavi Hezaveh <rezvan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#98898}

test/staging/explicit-resource-management/async-disposal-from-sync-method-returning-a-promise.js

@@ -0,0 +1,32 @@
+// Copyright (C) 2025 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: Fix async disposal from sync method returning a promise.
+includes: [asyncHelpers.js, compareArray.js]
+flags: [async]
+features: [explicit-resource-management]
+---*/
+
+asyncTest(async function() {
+  let values = [];
+
+  async function TestAsyncDisposalWithSyncMethodReturningAPromise() {
+    let stack = new AsyncDisposableStack();
+    const neverResolves = Promise.withResolvers().promise;
+    stack.use({
+      [Symbol.dispose]() {
+        return neverResolves
+      }
+    });
+    await stack.disposeAsync();
+    values.push(42);
+
+    await using x = {[Symbol.dispose]: () => neverResolves};
+    values.push(43);
+  };
+
+  await TestAsyncDisposalWithSyncMethodReturningAPromise();
+
+  assert.compareArray(values, [42, 43]);
+});