Add reachability functionality for android

[lavilaso]

It would be nice to have for android the equivalent of this, or failing that if it already exists, can someone tell me how to use it in my shared project?

[jamesmontemagno]

Please see documentation for Connectivity: https://docs.microsoft.com/en-us/xamarin/essentials/connectivity?context=xamarin%2Fxamarin-forms&tabs=android

and if you are looking for ping items see comments here: #334