Migrate Cordova config platform/plugin logic to using package.json

[imhoffd]

Cordova CLI 9.0.0 is no longer using config.xml for platform/plugin management.

We need to switch https://github.com/ionic-team/ionic-cli/blob/develop/packages/ionic/src/lib/integrations/cordova/config.ts to use package.json where applicable.

ref: apache/cordova-lib#750