Incorrect use of --directory param

# 🐞 Bug report

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

- [x] new
- [ ] build
- [ ] serve
- [ ] test
- [ ] e2e
- [ ] generate
- [ ] add
- [ ] update
- [ ] lint
- [ ] extract-i18n
- [ ] run
- [ ] config
- [ ] help
- [ ] version
- [ ] doc

### Is this a regression?

No, this issue has been in the CLI for a long time

### Description

When using the `--directory` param with the absolute path, the CLI does not respect the value and creates the directory path relative to the current directory instead.

## 🔬 Minimal Reproduction

Run the following command:

```shell
ng new app1 --directory=/tmp/app1 --skip-install
```

Expected behaviour:

The application is generated within `/tmp/app1` directory.

Actual behaviour:

The application is generated within current directory: `./tmp/app1`

## 🌍 Your Environment

Angular CLI: 11.0.2

Node: 14.15.0

OS: darwin x64

Angular: 

... 

Ivy Workspace: 

Package                      Version

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

@angular-devkit/architect    0.1100.2 (cli-only)

@angular-devkit/core         11.0.2 (cli-only)

@angular-devkit/schematics   11.0.2 (cli-only)

@schematics/angular          11.0.2 (cli-only)

@schematics/update           0.1100.2 (cli-only)

**Anything else relevant?**

Using macOS

首先，使用回報的 Angular CLI 版本重現 `ng new app1 --directory=/tmp/app1 --skip-install`，然後追蹤處理 `new` 及其 `--directory` 選項的 CLI 進入點。完成的標準是在 `/tmp/app1` 建立絕對目錄，而不是建立在 `./tmp/app1`，同時不影響相對路徑。

由索引模型根據 Issue 內容生成。