fix(aio): support ValueModule symbols in the TypeScript source (#14464)

In #14388 the following syntax is used in the source:

```
import * as view_utils from './linker/view_utils';
import * as viewEngine from './view/index';
…
export {view_utils as ɵview_utils};
export {viewEngine as ɵviewEngine};
```

The usage of `export {... as ...}` was not being recognised by dgeni.

It is now being recognised and a temporary dummy output file is being
rendered. Later we will either ignore this doctype altogether or find
a better way of rendering it.

aio/transforms/templates/value-module.template.html

@@ -0,0 +1 @@
+{% extends 'interface.template.html' %}