Disable package validation for libtorch packages

These don't contain managed surface area so running APICompat doesn't
provide much value.  Disable it to reduce the time spent and eliminate
the need to record and restore previous versions of libtorch.

Author: ericstj

Directory.Build.props

@@ -87,7 +87,7 @@
   <!-- we manually update these -->
   <PropertyGroup Condition="'$(MSBuildProjectName.IndexOf(`libtorch-`))' != '-1'">
     <LibTorchPackageVersion>2.2.1.1</LibTorchPackageVersion>
-    <PreviousPackageVersion>2.2.1.1</PreviousPackageVersion>
+    <EnablePackageValidation>false</EnablePackageValidation>
     <VersionPrefix>$(LibTorchPackageVersion)</VersionPrefix>
     <VersionSuffix></VersionSuffix>
   </PropertyGroup>

pkg/Directory.Build.targets

@@ -1,7 +1,7 @@
 <Project>
   <Import Project="..\Directory.Build.targets" />
 
-  <PropertyGroup Condition="'$(IsPackable)' != 'false'">
+  <PropertyGroup Condition="'$(IsPackable)' != 'false' and '$(EnablePackageValidation)' != 'false'">
     <EnablePackageValidation>true</EnablePackageValidation>
     <PackageValidationBaselineVersion>$(PreviousPackageVersion)</PackageValidationBaselineVersion>
   </PropertyGroup>