When using `loadChildren` or `loadComponent`, a common pattern is to pass
a function that returns a `Promise` from a dynamic import:
```typescript
{
path: 'lazy',
loadComponent: () => import('./lazy-file').then(m => m.LazyCmp),
}
```
The `.then` part of the expression selects the particular exported
component symbol from the dynamically imported ES module.
ES modules can have a "default export", created with the `export default`
modifier:
```typescript
@Component({...})
export default class LazyCmp { ... }
```
This default export is made available to dynamic imports under the well-
known key of `'default'`, per the ES module spec:
https://tc39.es/ecma262/#table-export-forms-mapping-to-exportentry-records
This commit adds a feature to the router to automatically dereference such
default exports. With this logic, when `export default` is used, a `.then`
operation to select the particular exported symbol is no longer required:
```typescript
{
path: 'lazy',
loadComponent: () => import('./lazy-file'),
}
```
The above `loadComponent` operation will automatically use the `default`
export of the `lazy-file` ES module.
This functionality works for `loadChildren` as well.
PR Close#47586
