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.

首先运行 `ng generate webWorker my-module/myWorker --project my-lib`，并跟踪 generate 命令的项目类型验证过程。完成的标准是：该命令能够为库项目生成 Web Worker，而不是报告 worker 需要应用程序。

由索引模型根据 Issue 内容生成。