Build errors when updating nuget packages.

[jgold6]

A customer reported that after updating the nuget packages, the build was failing.

I traced the errors down to three changes in Xamarin.Essentials:

1. DataTransfer type was renamed to Share
2. Clipboard.SetText(...) was renamed to Clipboard.SetTextAsync(...)
3. Connectivity.ConnectivityChanged event handler signature was changed from:
   protected async void ConnectivityChanged (ConnectivityChangedEventArgs e)
   to
   protected async void ConnectivityChanged (object sender, ConnectivityChangedEventArgs e)