Feature Request: Add support for cordova PreferredContentMode setting

With Cordova iOS v6.1.0, a new preference [**PreferredContentMode**](https://cordova.apache.org/announcements/2020/06/23/cordova-ios-6.1.0.html) is added for use. This setting allows developers to set [preferredContentMode](https://developer.apple.com/documentation/webkit/wkwebpagepreferences/3194426-preferredcontentmode) configuration for WKWebView available in iOS 13.0 and newer versions.

At present, adding iOS platform using `ionic cordova platform add ios` creates a CordovaLib project with CDVWebViewEngine.m in Private/Plugins directory that provides usage for this setting. Although, this code will not execute unless cordova-plugin-ionic-webview is removed from plugins. Once removed from plugins, the platform can be detected properly on iPadOS 13+ when `mobile` value is provided for `PreferredContentMode` preference in config.xml. In other cases, the platform is detected as desktop web browser.