fix(@angular/cli): ng doc doesn't open browser in Windows

In Windows, `process.exit` was being called prior of opening the browser which caused the browser never to open.

Closes #23105

(cherry picked from commit f99c08c)

packages/angular/cli/lib/init.ts

@@ -107,7 +107,7 @@ import { VERSION } from '../src/utilities/version';
     });
   })
   .then((exitCode: number) => {
-    process.exit(exitCode);
+    process.exitCode = exitCode;
   })
   .catch((err: Error) => {
     // eslint-disable-next-line  no-console