perf(@angular-devkit/build-angular): use esbuild-based builder to directly downlevel for await...of

esbuild 0.15.6 now supports transforming `for await..of` syntax and will now be used instead of babel
when the syntax is found within code that will be bundled. Zone.js requires that all async/await
related code be downleveled to properly hook promise callbacks. esbuild does not yet support
transforming async generators and so babel is still used when async generator syntax is detected
in an input file.
esbuild 0.15.6 also adjusted the `supported` option to imply that all dependent features of a
disabled feature are disabled as well. For the CLI, this allows only needing to specify that
`async-await` is disabled in the esbuild options.

Author: clydin

packages/angular_devkit/build_angular/src/builders/browser-esbuild/compiler-plugin.ts

@@ -342,7 +342,7 @@ export function createCompilerPlugin(
           }
 
           const data = typescriptResult.content ?? '';
-          const forceAsyncTransformation = /for\s+await\s*\(|async\s+function\s*\*/.test(data);
+          const forceAsyncTransformation = /async\s+function\s*\*/.test(data);
           const useInputSourcemap =
             pluginOptions.sourcemap &&
             (!!pluginOptions.thirdPartySourcemaps || !/[\\/]node_modules[\\/]/.test(args.path));
@@ -388,8 +388,7 @@ export function createCompilerPlugin(
       build.onLoad({ filter: /\.[cm]?js$/ }, async (args) => {
         const data = await fs.readFile(args.path, 'utf-8');
         const forceAsyncTransformation =
-          !/[\\/][_f]?esm2015[\\/]/.test(args.path) &&
-          /for\s+await\s*\(|async\s+function\s*\*/.test(data);
+          !/[\\/][_f]?esm2015[\\/]/.test(args.path) && /async\s+function\s*\*/.test(data);
         const shouldLink = await requiresLinking(args.path, data);
         const useInputSourcemap =
           pluginOptions.sourcemap &&

packages/angular_devkit/build_angular/src/builders/browser-esbuild/index.ts

@@ -259,15 +259,11 @@ async function bundleCode(
     target: 'es2020',
     supported: {
       // Native async/await is not supported with Zone.js. Disabling support here will cause
-      // esbuild to downlevel async/await to a Zone.js supported form.
+      // esbuild to downlevel async/await and for await...of to a Zone.js supported form. However, esbuild
+      // does not currently support downleveling async generators. Instead babel is used within the JS/TS
+      // loader to perform the downlevel transformation.
+      // NOTE: If esbuild adds support in the future, the babel support for async generators can be disabled.
       'async-await': false,
-      // Zone.js also does not support async generators or async iterators. However, esbuild does
-      // not currently support downleveling either of them. Instead babel is used within the JS/TS
-      // loader to perform the downlevel transformation. They are both disabled here to allow
-      // esbuild to handle them in the future if support is ever added.
-      // NOTE: If esbuild adds support in the future, the babel support for these can be disabled.
-      'async-generator': false,
-      'for-await': false,
     },
     mainFields: ['es2020', 'browser', 'module', 'main'],
     conditions: ['es2020', 'es2015', 'module'],