Fix Xamarin test projects.

Author: yfakariya

test/MsgPack.UnitTest.Xamarin.Android/MsgPack.UnitTest.Xamarin.Android.csproj

@@ -18,6 +18,8 @@
   </PropertyGroup>
   <Import Project="..\..\MsgPack.Common.props" />
   <PropertyGroup>
+    <SignAssembly>true</SignAssembly>
+    <DefineConstants>$(DefineConstants);XAMARIN;NUNITLITE;NETSTANDARD2_0;FEATURE_TAP;FEATURE_CONCURRENT;FEATURE_POINTER_CONVERSION;FEATURE_MEMCOPY</DefineConstants>
     <DocumentationFile></DocumentationFile>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">

test/MsgPack.UnitTest.Xamarin.iOS/MsgPack.UnitTest.Xamarin.iOS.csproj

@@ -12,6 +12,8 @@
   </PropertyGroup>
   <Import Project="..\..\MsgPack.Common.props" />
   <PropertyGroup>
+    <SignAssembly>true</SignAssembly>
+    <DefineConstants>$(DefineConstants);XAMARIN;NUNITLITE;NETSTANDARD2_0;FEATURE_TAP;FEATURE_CONCURRENT;FEATURE_POINTER_CONVERSION;FEATURE_MEMCOPY</DefineConstants>
     <DocumentationFile></DocumentationFile>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|iPhoneSimulator' ">