Work against .NET SDK update ManagePackageVersionsCentrally change

.NET SDK 8.0.300 changed ManagePackageVersionsCentrally to be implicitly set if Directory.Packages.props exists. We do not want this, as we intentionally have some projects that have it disabled.

We now explicitly unset the value in the Directory.Packages.props file to get the old behavior back.

See dotnet/core#9309

Directory.Packages.props

@@ -1,4 +1,14 @@
 <Project>
+  <PropertyGroup>
+    <!--
+    We actually set ManagePackageVersionsCentrally manually in another import file.
+    Since .NET SDK 8.0.300, ManagePackageVersionsCentrally is automatically set if Directory.Packages.props exists.
+    https://github.com/NuGet/NuGet.Client/pull/5572
+    We actively negate this here, as we have some packages in tree we don't want such automatic behavior for.
+    We use Directory.Build.props to get copy the state *after* our MSBuild config but before Nuget's config.
+    -->
+    <ManagePackageVersionsCentrally />
+  </PropertyGroup>
   <ItemGroup>
     <PackageVersion Include="BenchmarkDotNet" Version="0.13.12" />
     <PackageVersion Include="DiscordRichPresence" Version="1.2.1.24" />