Fixes issue introduced in https://github.com/angular/angular/pull/33808 for ng_rollup_bundle with `-spawn_strategy=standalone`. Without the sandbox (if --spawn_strategy=standalone is set) rollup can resolve to the non-esm .js file generated by ts_library instead of the desired .mjs. This fixes the problem by prioritizing .mjs.
Issue observed is of the flavor:
```
ERROR: modules/benchmarks/src/views/BUILD.bazel:20:1: Bundling JavaScript modules/benchmarks/src/views/bundle.es2015.js
[rollup] failed (Exit 1)
[!] Error: 'enableProdMode' is not exported by bazel-out/darwin-fastbuild/bin/packages/core/index.js
https://rollupjs.org/guide/en/#error-name-is-not-exported-by-module
bazel-out/darwin-fastbuild/bin/modules/benchmarks/src/views/index.mjs (12:9)
10: * found in the LICENSE file at https://angular.io/license
11: */
12: import { enableProdMode } from '@angular/core';
^
13: import { platformBrowser } from '@angular/platform-browser';
14: import { ViewsBenchmarkModuleNgFactory } from './views-benchmark.ngfactory';
Error: 'enableProdMode' is not exported by bazel-out/darwin-fastbuild/bin/packages/core/index.js
```
PR Close#33867
91a2506c82