CLI generates items in unexpected workspace directories

# 🐞 Bug report

### Command

- [x] generate

### Description

In a multi-project workspace, `ng generate` creates items (components, etc.) based on the current directory, rather than `[ProjectRoot]/src/app` or `[ProjectRoot/src/lib`.

In a single-project workspace, the CLI knows to place items inside of `src...`. However, in a multi-project workspace with a `projects/...` directory structure, the developer must navigate to `src/app` or `src/lib` prior to generating the item, or specify its location, such as:
```
cd ./projects/app1/src/app
ng generate component component1
```

or

```
cd ./projects/app1
ng generate component src/app/component1 -module src/app/app
```

The expectation would be to navigate to the root of the project, then generate items in the same manner as a single-project workspace, such as:

```
cd ./projects/app1
ng generate component component1
```

Ideally, developers would not have to worry about where they are within the project directory structure or having to specify the location of the module (particularly in default module configurations).

## 🌍 Your Environment

Angular CLI: 12.2.2

Node: 14.16.0

Package Manager: npm 7.21.0

OS: win32 x64


Angular: 12.2.2

... animations, cdk, cli, common, compiler, compiler-cli, core

... forms, material, platform-browser, platform-browser-dynamic

... router

Package                         Version

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

@angular-devkit/architect       0.1202.2

@angular-devkit/build-angular   12.2.2

@angular-devkit/core            12.2.2

@angular-devkit/schematics      12.2.2

@schematics/angular             12.2.2

ng-packagr                      12.2.0

rxjs                            6.6.7

typescript                      4.3.5

首先，在多项目 workspace 中重现 `ng generate component component1` 命令，比较从项目根目录生成与从 `src/app` 或 `src/lib` 生成的结果。完成的标准是：从项目根目录生成时，项目项会放置在预期的项目源目录下，并且无需显式路径即可解析模块。

由索引模型根据 Issue 内容生成。