Update version to 4.0 for feature branch (dotnet#6743)

Author: JakeRadMSFT

eng/Versions.props

@@ -9,7 +9,7 @@
         https://github.com/dotnet/arcade/blob/c788ffa83b088cafe9dbffc1cbc8155ba88b2553/Documentation/CorePackages/Versioning.md#output
     -->
     <DotNetUseShippingVersions>true</DotNetUseShippingVersions>
-    <VersionPrefix>3.0.0</VersionPrefix>
+    <VersionPrefix>4.0.0</VersionPrefix>
     <PreReleaseVersionLabel>preview</PreReleaseVersionLabel>
     <AssemblyVersion>1.0.0.0</AssemblyVersion>
     <!-- .NET Runtime product dependencies -->