[monodroid] Use CoreFX to implement System.Drawing types that used to be in Mono.Android.dll (#13135)
* [monodroid] Use CoreFX to fill in reference stubs for System.Drawing types that are currently 'forked' from Mono into Mono.Android.dll
The list of localy implemented System.Drawing types: https://github.com/xamarin/xamarin-android/blob/
e0da1f152de84c4cc39983f2fda775ec98c08250/src/Mono.Android/Mono.Android.csproj#L311-L325
* [netstandard] Update for Mono.Android change
* Bump reference assemblies to include Mono.Android update
* Use System.Drawing.Common to find moved types in monodroid case for netstandard facade
* Bump API snapshot submodule
* [csproj] Update project files