Duplicate Java Callable Wrapper names are allowed when they shouldn't be.

[jonpryor]

Steps to Reproduce

1. Create a solution consisting of three projects: App.csproj, Lib1.csproj, Lib2.csproj, in which App.csproj references both Lib1.csproj and Lib2.csproj.

2. Add the following file to both Lib1.csproj and Lib2.csproj:

   using System;
   using Android.Runtime;
   
   namespace Lib1
   {
     [Register("examplelib.EmptyClass")]
     public class EmptyClass : Java.Lang.Object
     {
     }
   }

3. Create an .apk: msbuild /t:SignAndroidPackage App.csproj

Expected Behavior

It should error out, as we have two assemblies which will each generate an example lib.EmptyClass Java type.

Actual Behavior

Warnings:

warning : Duplicate managed type found! Mappings between managed types and Java types must be unique. First Type: 'Lib1.EmptyClass, Lib1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'; Second Type: 'Lib1.EmptyClass, Lib2, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.
warning : References to the type 'Lib1.EmptyClass' will refer to 'Lib1.EmptyClass, Lib1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null'.

Discussion:

The warning is correct, in that it should be emitted. However, because we emit that warning, we don't check for duplicate Java Callable Wrapper names. The problem is here:

https://github.com/xamarin/xamarin-android/blob/5c80b4b260981cf16d74cdcbc8dfc4215c01ec83/src/Xamarin.Android.Build.Tasks/Tasks/GenerateJavaStubs.cs#L188

[jonathanpeppers]

I started working on this as an "easy win" during triage today, but @brendanzagaeski should probably finish this up: master...jonathanpeppers:dupe-jcws

As part of: #2258 (comment)