Library schematic does not support path property

# 🐞 Bug report

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

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

### Is this a regression?

Not as far as I know

### Description

I tried to create a schematic that generates an application and adds a library to it. However, the library schematic does not accept a `path` as parameter and it then attempts to create the library in the folder that contains the application. Specifically, it tries to read the `angular.json` file from the folder containing the application folder (e.g. the folder where the schematic is run).

Note that I expected the `path` property to work, as it's included with most of the other Angular schematics, for example component, module and service.

## 🔬 Minimal Reproduction

A minimal reproduction may be found [in this repo](https://github.com/CobusKruger/AngularProjectMergeIssues).

It also addresses a problem I had when trying to work around this with `applyToSubtree`.

Here is the simplest description I could come up with.

Given this factory:

```typescript
export function createProject(_options: any): Rule {
return (_tree: Tree, _context: SchematicContext) => {
return chain([
externalSchematic('@schematics/angular', 'ng-new', optionsNew),
externalSchematic('@schematics/angular', 'library', optionsLib)
]);
};
}
```

If you execute the schematic in a folder named `/parent/folder` and the app generates in a new folder named app (`/parent/folder/app`), the library schematic searches for the `angular.json` in `/parent/folder` instead of `/parent/folder/app`.

## 🔥 Exception or Error
```
An error occured:
Error: Unable to locate a workspace file for workspace path.
at Object.readWorkspace (C:\dev\scratchpad\scaffolding-tests\node_modules\@angular-devkit\core\src\workspace\core.js:74:19)
at async Object.getWorkspace (C:\dev\scratchpad\scaffolding-tests\node_modules\@schematics\angular\utility\workspace.js:51:27)
at async C:\dev\scratchpad\scaffolding-tests\node_modules\@schematics\angular\library\index.js:153:27
```

## 🌍 Your Environment

     _                      _                 ____ _     ___

    / \   _ __   __ _ _   _| | __ _ _ __     / ___| |   |_ _|

   / △ \ | '_ \ / _` | | | | |/ _` | '__|   | |   | |    | |

  / ___ \| | | | (_| | |_| | | (_| | |      | |___| |___ | |

 /_/   \_\_| |_|\__, |\__,_|_|\__,_|_|       \____|_____|___|

                |___/

    


Angular CLI: 8.3.1

Node: 12.12.0

OS: win32 x64

Angular: undefined

...

Package                      Version

------------------------------------------------------

@angular-devkit/architect    0.803.1 (cli-only)

@angular-devkit/core         8.3.17

@angular-devkit/schematics   8.3.17

@schematics/angular          8.3.1 (cli-only)

@schematics/update           0.803.1 (cli-only)

rxjs                         6.4.0

typescript                   3.5.3

## Similar issues
https://github.com/angular/angular-cli/issues/17598

从 issue 中链接的最小复现仓库开始，跟踪 @schematics/angular/library/index.js 中的 library schematic 入口点，以及错误堆栈中的 utility/workspace.js。确认应用程序在子文件夹中生成时路径是如何处理的。当 library schematic 接受该路径，并且能够在没有 workspace 错误的情况下找到生成的应用程序的 angular.json 时，即表示完成。

由索引模型根据 Issue 内容生成。