Fix Android build on macOS

copy /Y does not work on macOS. Using an MSBuild Copy task instead.

(cherry picked from commit 9befdd2e0300de0ad627a763a38903647e9dd495)

LibVLCSharp.Android.AWindow/LibVLCSharp.Android.AWindow.csproj

@@ -50,14 +50,5 @@
     <TransformFile Include="Transforms\EnumMethods.xml" />
   </ItemGroup>
   <Import Project="$(MSBuildExtensionsPath)\Xamarin\Android\Xamarin.Android.Bindings.targets" />
-  <PropertyGroup>
-    <PostBuildEvent>copy /Y "$(TargetDir)$(ProjectName).dll" "$(ProjectDir)..\LibVLCSharp\bin\$(ConfigurationName)\monoandroid81\$(ProjectName).dll"</PostBuildEvent>
-  </PropertyGroup>
-  <!-- To modify your build process, add your task inside one of the targets below and uncomment it. 
-       Other similar extension points exist, see Microsoft.Common.targets.
-  <Target Name="BeforeBuild">
-  </Target>
-  <Target Name="AfterBuild">
-  </Target>
-  -->
+  <Import Project="copy.targets" />
 </Project>
\ No newline at end of file

LibVLCSharp.Android.AWindow/copy.targets

+<Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">  
+    <Target Name="PostBuild" AfterTargets="PostBuildEvent">  
+        <Copy 
+            SourceFiles="$(TargetDir)$(ProjectName).dll"  
+            DestinationFolder="$(ProjectDir)..\LibVLCSharp\bin\$(ConfigurationName)\monoandroid81" />  
+    </Target>
+</Project>
\ No newline at end of file