ionic cordova prepare --watch flag does not exist

**Description:**
when trying to using `ionic cordova prepare ios --watch` the following error is thrown:

`Unknown option: '--watch'`

**My `ionic info`:**
```
Ionic:

Ionic CLI : 5.4.13 (/usr/local/lib/node_modules/ionic)
Ionic Framework : @ionic/angular 4.11.7
@angular-devkit/build-angular : 0.801.3
@angular-devkit/schematics : 8.1.3
@angular/cli : 8.1.3
@ionic/angular-toolkit : 2.1.1

Cordova:

Cordova CLI : 9.0.0 (cordova-lib@9.0.1)
Cordova Platforms : ios 5.1.1
Cordova Plugins : cordova-plugin-ionic-keyboard 2.2.0, cordova-plugin-ionic-webview 4.1.3, (and 5 other plugins)

Utility:

cordova-res : 0.8.1
native-run (update available: 0.3.0) : 0.2.9

System:

ios-deploy : 1.9.2
ios-sim : 8.0.2
NodeJS : v12.4.0 (/usr/local/Cellar/node/12.4.0/bin/node)
npm : 6.13.2
OS : macOS Catalina
Xcode : Xcode 11.2.1 Build version 11B53
```

Reproduce `ionic cordova prepare ios --watch` using the reported Ionic CLI and Cordova versions, then trace how the prepare command validates options. Confirm whether `--watch` is intended to be supported and document the expected behavior or failure condition once the command handling is understood.

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