[Microsoft.Android.Build.BaseTasks] add StrongName (#127)

* Bump to LibZipSharp 2.0.0-alpha8
* Fix weird error about LibZipSharp, by multi-targeting

Author: dellis1972

src/Microsoft.Android.Build.BaseTasks/MSBuildReferences.projitems

@@ -5,7 +5,7 @@
   <!--Import this file in projects needing to reference Microsoft.Build.*.dll -->
   <PropertyGroup>
     <MSBuildPackageReferenceVersion>16.10.0</MSBuildPackageReferenceVersion>
-    <LibZipSharpVersion>2.0.0-alpha7</LibZipSharpVersion>
+    <LibZipSharpVersion>2.0.0-alpha8</LibZipSharpVersion>
     <MonoUnixVersion>7.0.0-alpha8.21302.6</MonoUnixVersion>
   </PropertyGroup>
 
@@ -15,7 +15,7 @@
     <PackageReference Include="Microsoft.Build.Tasks.Core"     Version="$(MSBuildPackageReferenceVersion)" />
     <PackageReference Include="Microsoft.Build.Utilities.Core" Version="$(MSBuildPackageReferenceVersion)" />
     <PackageReference Include="K4os.Compression.LZ4" Version="1.1.11" />
-    <PackageReference Include="Xamarin.Build.AsyncTask" Version="0.3.4" GeneratePathProperty="true" />
+    <PackageReference Include="Xamarin.Build.AsyncTask" Version="0.4.0" GeneratePathProperty="true" />
     <PackageReference Include="Xamarin.LibZipSharp" Version="$(LibZipSharpVersion)" GeneratePathProperty="true" />
     <PackageReference Include="Mono.Unix" Version="$(MonoUnixVersion)" GeneratePathProperty="true" />
   </ItemGroup>

src/Microsoft.Android.Build.BaseTasks/Microsoft.Android.Build.BaseTasks.csproj

@@ -4,11 +4,13 @@
   <Import Project="..\tools\BuildTasks.props" Sdk="Microsoft.DotNet.Arcade.Sdk" />
 
   <PropertyGroup>
-    <TargetFramework>netstandard2.0</TargetFramework>
+    <TargetFrameworks>netstandard2.0;netcoreapp3.1</TargetFrameworks>
     <RootNamespace>Microsoft.Android.Build.Tasks</RootNamespace>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <GenerateResxSource>true</GenerateResxSource>
     <UpdateXlfOnBuild Condition=" '$(RunningOnCI)' != 'true' ">true</UpdateXlfOnBuild>
+    <SignAssembly>true</SignAssembly>
+    <AssemblyOriginatorKeyFile>..\..\product.snk</AssemblyOriginatorKeyFile>
   </PropertyGroup>
 
   <ItemGroup>