Support web workers in libraries

# 🚀 Feature request

### Command (mark with an `x`)

```
- [ ] new
- [ ] build
- [ ] serve
- [ ] test
- [ ] e2e
- [x] generate
- [ ] add
- [ ] update
- [ ] lint
- [ ] xi18n
- [ ] run
- [ ] config
- [ ] help
- [ ] version
- [ ] doc
```

### Description
I would like to use Web Workers in an Angular 8 library project.
In version 8.1.1 this seems to be supported for project type 'application' only:
```console
ng generate webWorker my-module/myWorker --project my-lib
Web Worker requires a project type of "application".
```

### Describe the solution you'd like
Generating a Web Worker should work for project type 'library' as well.

### Describe alternatives you've considered
Rewrite TypeScript worker code to JavaScript file.

Commencez par exécuter `ng generate webWorker my-module/myWorker --project my-lib` et suivez la validation du type de projet du comando generate. C’est terminé lorsque la commande génère un Web Worker pour un projet de bibliothèque au lieu d’indiquer que les workers nécessitent une application.

Rédigé par le modèle d'indexation à partir du texte de l'issue.