'ng update' does not work with yarn workspaces

# 🐞 Bug report

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

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

### Is this a regression?

No

### Description

I am utilizing yarn workspaces -feature in my project. Problem is that I have to keep Angular & AngularCLI dependencies on root packages.json, otherwise 'ng update' command can't figure out the version I currently have. I'd rather keep root package.json clean and move Angular & CLI dependencies to project/package.json to keep things isolated.
Looking at the [code](https://github.com/angular/angular-cli/blob/af93227f3295e918771e018d7d0fabbef774f1d1/packages/angular/cli/commands/update-impl.ts#L123), update command resolves dependencies from root package, even when command is executed on package folder. Would it be possible to change behavior in a way that update would first check package dependencies and the fall back to root if nothing is found?

## 🔬 Minimal Reproduction

- init yarn workspace project as follows: https://yarnpkg.com/lang/en/docs/workspaces/
- init angular app with cli and move dependencies from root package.json to workspace-a/package.json (example from previous step)
- wait until new angular version is available
- cd to 'workspace-a' and run 'ng update'. Command fails to find any dependencies to update.

## 🔥 Exception or Error

N/A

## 🌍 Your Environment

Angular CLI: 8.0.3

Node: 10.15.3

OS: win32 x64

Angular: 8.0.1

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

... language-service, platform-browser, platform-browser-dynamic

... router, service-worker


Package                           Version

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

@angular-devkit/architect         0.800.3

@angular-devkit/build-angular     0.800.3

@angular-devkit/build-optimizer   0.800.3

@angular-devkit/build-webpack     0.800.3

@angular-devkit/core              8.0.3

@angular-devkit/schematics        8.0.3

@angular/cli                      8.0.3

@angular/pwa                      0.800.3

@ngtools/webpack                  8.0.3

@schematics/angular               8.0.3

@schematics/update                0.800.3

rxjs                              6.4.0

typescript                        3.4.5

webpack                           4.30.0

Root package.json:

  "dependencies": {},

  "devDependencies": {

    "npm-run-all": "^4.1.5"

  },

'workspace-a/package.json':

"dependencies": {

    "@angular/animations": "~8.0.1",

    "@angular/common": "~8.0.1",

    "@angular/compiler": "~8.0.1",

    "@angular/core": "~8.0.1",

    "@angular/forms": "~8.0.1",

    "@angular/platform-browser": "~8.0.1",

    "@angular/platform-browser-dynamic": "~8.0.1",

    "@angular/pwa": "^0.800.3",

    "@angular/router": "~8.0.1",

    "@angular/service-worker": "~8.0.1",

    "@auth0/angular-jwt": "^2.1.0",

    "@ngx-translate/core": "^11.0.1",

    ...

    "rxjs": "~6.4.0",

    "tslib": "^1.9.0",

    "zone.js": "~0.9.1"

  },

  "devDependencies": {

    "@angular-devkit/build-angular": "~0.800.0",

    "@angular/cli": "~8.0.3",

    "@angular/compiler-cli": "~8.0.1",

    "@angular/language-service": "~8.0.1",

    ...

  }

**Anything else relevant?**

まず、123行目付近の packages/angular/cli/commands/update-impl.ts にリンクされている update コマンドの実装から始め、Angular の依存関係を workspace-a/package.json にのみ配置した Yarn workspace を使って失敗を再現します。workspace ディレクトリから依存関係の解決がどのように行われるかを確認します。ng update が root package.json に依存関係を配置しなくても workspace の Angular 依存関係を見つけて更新できれば完了です。

索引モデルが issue の本文から書いたものです。