fix(runtime): align async iterator throw with Babel (#28059)

Async-from-sync `.throw(error)` currently looks up the sync iterator's `return` method. Change that lookup to `throw` in both CommonJS and ESM helpers, matching [Babel's implementation](https://github.com/babel/babel/blob/main/packages/babel-helpers/src/helpers/asyncIterator.ts).

The upstream `yield-star/throw-method-sync-iterator` regression added in #28057 now passes; update its execution snapshot. `just test-transform` reproduces the expected results: 320/418 Babel execution tests and 40/42 local execution tests, with no new failures. Direct delegation checks also pass for both helper formats.

npm/runtime/src/helpers/asyncIterator.js

@@ -37,7 +37,7 @@ function AsyncFromSyncIterator(r) {
       }) : AsyncFromSyncIteratorContinuation(n.apply(this.s, arguments));
     },
     "throw": function _throw(r) {
-      var n = this.s["return"];
+      var n = this.s["throw"];
       return void 0 === n ? Promise.reject(r) : AsyncFromSyncIteratorContinuation(n.apply(this.s, arguments));
     }
   }, new AsyncFromSyncIterator(r);

npm/runtime/src/helpers/esm/asyncIterator.js

@@ -37,7 +37,7 @@ function AsyncFromSyncIterator(r) {
       }) : AsyncFromSyncIteratorContinuation(n.apply(this.s, arguments));
     },
     "throw": function _throw(r) {
-      var n = this.s["return"];
+      var n = this.s["throw"];
       return void 0 === n ? Promise.reject(r) : AsyncFromSyncIteratorContinuation(n.apply(this.s, arguments));
     }
   }, new AsyncFromSyncIterator(r);

tasks/transform_conformance/snapshots/babel_exec.snap.md

@@ -2,7 +2,7 @@ commit: a56fe4a4
 
 node: v26.12.1
 
-Passed: 319 of 418 (76.32%)
+Passed: 320 of 418 (76.56%)
 
 Failures:
 
@@ -24,14 +24,6 @@ AssertionError: expected { value: 2, done: true } to deeply equal { value: 4, do
     at test (./tasks/transform_conformance/fixtures/babel/babel-plugin-transform-async-generator-functions-test-fixtures-async-generators-await-in-finally-exec.test.js:28:44)
     at process.processTicksAndRejections (node:internal/process/task_queues:104:5)
 
-./fixtures/babel/babel-plugin-transform-async-generator-functions-test-fixtures-yield-star-throw-method-sync-iterator-exec.test.js
-AssertionError: expected [ Array(3) ] to deeply equal [ 'next', 'throw:TEST', …(1) ]
-    at ./tasks/transform_conformance/fixtures/babel/babel-plugin-transform-async-generator-functions-test-fixtures-yield-star-throw-method-sync-iterator-exec.test.js:57:16
-    at Generator.next (<anonymous>)
-    at asyncGeneratorStep (./npm/runtime/src/helpers/asyncToGenerator.js:3:17)
-    at _next (./npm/runtime/src/helpers/asyncToGenerator.js:17:9)
-    at process.processTicksAndRejections (node:internal/process/task_queues:104:5)
-
 ./fixtures/babel/babel-plugin-transform-async-to-generator-test-fixtures-async-to-generator-async-complex-params-exec.test.js
 TypeError: Cannot destructure property 'b' of 'undefined' as it is undefined.
     at Object.foo (./tasks/transform_conformance/fixtures/babel/babel-plugin-transform-async-to-generator-test-fixtures-async-to-generator-async-complex-params-exec.test.js:7:13)