Added .NET 5 target (and removed built-in package)

Author: Sergio0694

Microsoft.Toolkit.Mvvm/Microsoft.Toolkit.Mvvm.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
+    <TargetFrameworks>netstandard2.0;netstandard2.1;net5.0</TargetFrameworks>
     <LangVersion>9.0</LangVersion>
     <Nullable>enable</Nullable>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
@@ -20,18 +20,14 @@
   <!-- .NET Standard 2.0 doesn't have the Span<T> and IAsyncEnumerable<T> types -->
   <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
     <PackageReference Include="Microsoft.Bcl.AsyncInterfaces" Version="5.0.0" />
+    <PackageReference Include="System.ComponentModel.Annotations" Version="5.0.0" />
     <PackageReference Include="System.Memory" Version="4.5.4" />
   </ItemGroup>
 
   <!-- .NET Standard 2.1 doesn't have the Unsafe type -->
   <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.1' ">
-    <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="5.0.0" />
-  </ItemGroup>
-
-  <ItemGroup>
-    
-    <!--Needed to support the INotifyDataErrorInfo interface-->
     <PackageReference Include="System.ComponentModel.Annotations" Version="5.0.0" />
+    <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="5.0.0" />
   </ItemGroup>
 
 </Project>

UnitTests/UnitTests.NetCore/UnitTests.NetCore.csproj

@@ -16,7 +16,7 @@
 
   <!-- Workaround for the .NET Core 2.1 binary not resolving the Unsafe assembly properly -->
   <ItemGroup Condition=" '$(TargetFramework)' == 'netcoreapp2.1' ">
-    <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="4.7.1" />
+    <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="5.0.0" />
   </ItemGroup>
 
   <ItemGroup>