Conditionally enable/disable targeting pack tests (#20255)

Author: John Luo

src/Framework/test/Microsoft.AspNetCore.App.UnitTests.csproj

@@ -36,6 +36,10 @@
       <_Parameter1>TargetingPackLayoutRoot</_Parameter1>
       <_Parameter2>$(TargetingPackLayoutRoot)</_Parameter2>
     </AssemblyAttribute>
+    <AssemblyAttribute Include="Microsoft.AspNetCore.TestData">
+      <_Parameter1>IsTargetingPackBuilding</_Parameter1>
+      <_Parameter2>$(IsTargetingPackBuilding)</_Parameter2>
+    </AssemblyAttribute>
     <AssemblyAttribute Include="Microsoft.AspNetCore.TestData">
       <_Parameter1>VerifyAncmBinary</_Parameter1>
       <_Parameter2>$(VerifyAncmBinary)</_Parameter2>

src/Framework/test/TargetingPackTests.cs

@@ -20,17 +20,24 @@ public class TargetingPackTests
         private readonly string _expectedRid;
         private readonly string _targetingPackRoot;
         private readonly ITestOutputHelper _output;
+        private readonly bool _isTargetingPackBuilding;
 
         public TargetingPackTests(ITestOutputHelper output)
         {
             _output = output;
             _expectedRid = TestData.GetSharedFxRuntimeIdentifier();
             _targetingPackRoot = Path.Combine(TestData.GetTestDataValue("TargetingPackLayoutRoot"), "packs", "Microsoft.AspNetCore.App.Ref", TestData.GetTestDataValue("TargetingPackVersion"));
+            _isTargetingPackBuilding = bool.Parse(TestData.GetTestDataValue("IsTargetingPackBuilding"));
         }
 
-        [Fact(Skip="https://github.com/aspnet/AspNetCore/issues/14832")]
+        [Fact]
         public void AssembliesAreReferenceAssemblies()
         {
+            if (!_isTargetingPackBuilding)
+            {
+                return;
+            }
+
             IEnumerable<string> dlls = Directory.GetFiles(_targetingPackRoot, "*.dll", SearchOption.AllDirectories);
             Assert.NotEmpty(dlls);
 
@@ -55,9 +62,14 @@ public void AssembliesAreReferenceAssemblies()
             });
         }
 
-        [Fact(Skip="https://github.com/aspnet/AspNetCore/issues/14832")]
+        [Fact]
         public void PlatformManifestListsAllFiles()
         {
+            if (!_isTargetingPackBuilding)
+            {
+                return;
+            }
+
             var platformManifestPath = Path.Combine(_targetingPackRoot, "data", "PlatformManifest.txt");
             var expectedAssemblies = TestData.GetSharedFxDependencies()
                 .Split(';', StringSplitOptions.RemoveEmptyEntries)