[Rush]

A bundler without per-feature lowering (Rolldown's transform.target lowers by ES version) can't build an Angular app that runs zone.js the way the Angular CLI does: zone.js can't see native await, so the CLI's esbuild build turns async functions into generators (supported: { 'async-await': false }) and leaves everything else native. Lowering by target to ES2016 also lowers object spread, optional chaining and class fields.

transformForBrowser(code, filename, options) (and transformForBrowserSync) does just that, with oxc_transformer:

• async functions, async generators and for await become generators; helpers are imported from @oxc-project/runtime;
• TypeScript is stripped with Angular's settings: legacy decorators (experimentalDecorators), and useDefineForClassFields: false semantics, so fields are assigned in the constructor after parameter properties and statics after the class (as tsc and esbuild emit them);
• JavaScript keeps its class fields; only async is lowered;
• lowerAsync: false keeps async native (server rendering is zoneless).

We use it in a Rolldown plugin's transform hook, after transformAngularFile, for every TypeScript file and every JavaScript file that contains async; with it a production build of our app matches the Angular CLI's output.

Tests: three in crates/oxc_angular_compiler/src/browser.rs and five in napi/angular-compiler/test/transform-for-browser.test.ts (async lowering, lowerAsync: false, field order after parameter properties, legacy decorators, syntax errors). index.js and index.d.ts are regenerated.