As of Feb 2020, I had to install couple of androidx plugins to solve the issue. So simply run the following commands in your project root:
Add plugin to enable AndroidX in the project
cordova plugin add cordova-plugin-androidx
Add plugin to patch existing plugin source that uses the Android Support Library to use AndroidX
cordova plugin add cordova-plugin-androidx-adapter
Now run the following commands in your project root:
cordova clean
ionic cordova build android
Hope this helps someone!