Add avalonia version property to nuget package.

packages/Avalonia/Avalonia.csproj

@@ -5,6 +5,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+      <PackageReference Include="Avalonia.BuildServices" Version="0.0.2" />
       <ProjectReference Include="../../src/Avalonia.Remote.Protocol/Avalonia.Remote.Protocol.csproj" />
       <ProjectReference Include="../../src/Avalonia.Build.Tasks/Avalonia.Build.Tasks.csproj">
         <PrivateAssets>all</PrivateAssets>
@@ -60,4 +61,36 @@
   <Import Project="..\..\build\NetFX.props" />
   <Import Project="..\..\build\CoreLibraries.props" />
   <Import Project="..\..\build\SourceLink.props" Condition="'$(DisableSourceLink)' == ''" />
+
+  <UsingTask TaskName="WriteCurrentPackageVersionPropsTask" TaskFactory="RoslynCodeTaskFactory" AssemblyFile="$(MSBuildToolsPath)\Microsoft.Build.Tasks.Core.dll">
+    <ParameterGroup>
+      <Filename ParameterType="System.String" Required="true" />
+      <Version ParameterType="System.String" Required="true" />
+      <IsLocalCache ParameterType="System.Boolean" Required="false" />
+    </ParameterGroup>
+    <Task>
+      <Using Namespace="System" />
+      <Using Namespace="System.IO" />
+      <Code Type="Fragment" Language="cs">
+        <![CDATA[
+                File.WriteAllText(Filename, "<Project><PropertyGroup>" + 
+                "<AvaloniaMainPackageVersion>" + Version + "</AvaloniaMainPackageVersion>" +
+                "</PropertyGroup></Project>");
+]]>
+      </Code>
+    </Task>
+  </UsingTask>
+
+  <Target Name="WriteCurrentPackageVersionProps" BeforeTargets="_GetPackageFiles">
+    <PropertyGroup>
+      <PackageVersionPropsPath>$(IntermediateOutputPath)/AvaloniaVersion.props</PackageVersionPropsPath>
+    </PropertyGroup>
+    <WriteCurrentPackageVersionPropsTask Filename="$(PackageVersionPropsPath)" Version="$(PackageVersion)" />
+    <ItemGroup>
+      <Content Include="$(PackageVersionPropsPath)">
+        <Pack>true</Pack>
+        <PackagePath>build</PackagePath>
+      </Content>
+    </ItemGroup>
+  </Target>
 </Project>

packages/Avalonia/Avalonia.props

@@ -7,6 +7,7 @@
   </PropertyGroup>
   <Import Project="$(MSBuildThisFileDirectory)\AvaloniaBuildTasks.props"/>
   <Import Project="$(MSBuildThisFileDirectory)\Avalonia.Generators.props"/>
+  <Import Project="$(MSBuildThisFileDirectory)..\build\AvaloniaVersion.props" />
 
   <!-- Allow loading the AvaloniaVS extension when referencing the Avalonia nuget package -->
   <ItemGroup>