Centralize VersionPrefix information in Version.props (#2439)

eng/Versions.props

@@ -1,7 +1,15 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
   <PropertyGroup>
+    <!-- 
+      Primary version prefix for this repo - usually changes only once per major release
+    -->
     <VersionPrefix>4.8.1</VersionPrefix>
+    <!-- 
+      Version prefix used by a few projects like Project Templates
+      Revision portion of Major.Minor.Revision usually updated every release
+    -->
+    <TraditionalVersionPrefix>3.1.2</TraditionalVersionPrefix>
     <PreReleaseVersionLabel>servicing</PreReleaseVersionLabel>
     <DotNetUseShippingVersions>true</DotNetUseShippingVersions>
     <AssemblyVersion>4.0.0.0</AssemblyVersion>

packaging/Microsoft.Dotnet.Wpf.ProjectTemplates/Microsoft.DotNet.Wpf.ProjectTemplates.ArchNeutral.csproj

@@ -3,7 +3,7 @@
     <ProjectGuid>{BFF6C118-3369-43B5-ACA6-D65ED00EEBE0}</ProjectGuid>
     <TargetFramework>netcoreapp3.1</TargetFramework>
     <Platforms>AnyCPU;x64</Platforms>
-    <VersionPrefix>3.1.2</VersionPrefix>
+    <VersionPrefix>$(TraditionalVersionPrefix)</VersionPrefix>
   </PropertyGroup>
 
   <PropertyGroup>

packaging/Microsoft.NET.Sdk.WindowsDesktop/Microsoft.NET.Sdk.WindowsDesktop.ArchNeutral.csproj

@@ -3,7 +3,7 @@
     <ProjectGuid>{440d06b8-e3de-4c0d-ad25-cd4f43d836e1}</ProjectGuid>
     <TargetFramework>netcoreapp3.1</TargetFramework>
     <Platforms>AnyCPU;x64</Platforms>
-    <VersionPrefix>3.1.2</VersionPrefix>
+    <VersionPrefix>$(TraditionalVersionPrefix)</VersionPrefix>
   </PropertyGroup>
 
   <PropertyGroup>