Replace conditional compilation with partial classes

[AlvaroRojas]

🏗 Enhancement Proposal

The library today uses partial compilation to execute code for a specific platform. This is hard to debug as each platform might use different classes and methods to do the same thing as other platforms.

Pitch

I propose to move to partial classes for a cleaner class structure, easier debugging and easier future contributions to the project in the future.

Platforms affected (mark all that apply)

• [x] :iphone: iOS
• [x] :robot: Android
• [ ] :checkered_flag: WPF
• [x] :earth_americas: UWP
• [x] :apple: MacOS
• [x] :tv: tvOS
• [ ] :monkey: Xamarin.Forms