Update __awaiter to be more spec compliant (#32462)

* Update __awaiter to be more spec compliant

* Add awaiter evaluation test

src/compiler/transformers/es2017.ts

@@ -775,10 +775,11 @@ namespace ts {
         priority: 5,
         text: `
             var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, generator) {
+                function adopt(value) { return value instanceof P ? value : new P(function (resolve) { resolve(value); }); }
                 return new (P || (P = Promise))(function (resolve, reject) {
                     function fulfilled(value) { try { step(generator.next(value)); } catch (e) { reject(e); } }
                     function rejected(value) { try { step(generator["throw"](value)); } catch (e) { reject(e); } }
-                    function step(result) { result.done ? resolve(result.value) : new P(function (resolve) { resolve(result.value); }).then(fulfilled, rejected); }
+                    function step(result) { result.done ? resolve(result.value) : adopt(result.value).then(fulfilled, rejected); }
                     step((generator = generator.apply(thisArg, _arguments || [])).next());
                 });
             };`

src/testRunner/tsconfig.json

@@ -73,6 +73,7 @@
         "unittests/config/tsconfigParsing.ts",
         "unittests/evaluation/asyncArrow.ts",
         "unittests/evaluation/asyncGenerator.ts",
+        "unittests/evaluation/awaiter.ts",
         "unittests/evaluation/forAwaitOf.ts",
         "unittests/evaluation/objectRest.ts",
         "unittests/services/cancellableLanguageServiceOperations.ts",

src/testRunner/unittests/evaluation/awaiter.ts

@@ -0,0 +1,24 @@
+describe("unittests:: evaluation:: awaiter", () => {
+    // NOTE: This could break if the ECMAScript spec ever changes the timing behavior for Promises (again)
+    it("await (es5)", async () => {
+        const result = evaluator.evaluateTypeScript(`
+        async function a(msg: string) {
+            await Promise.resolve();
+            output.push(msg);
+        }
+        function b(msg: string) {
+            return Promise.resolve().then(() => {
+                output.push(msg);
+            });
+        }
+        export const output: string[] = [];
+        export async function main() {
+            const p1 = a('1');
+            const p2 = b('2');
+            await Promise.all([p1, p2]);
+        }
+        `);
+        await result.main();
+        assert.deepEqual(result.output, ["1", "2"]);
+    });
+});