Replace obsolete nuget api in Microsoft.DotNet.PackageValidation (#42508)

Author: akoeplinger

src/Compatibility/ApiCompat/Microsoft.DotNet.PackageValidation/Package.cs

@@ -94,11 +94,11 @@ public Package(string packagePath,
             _contentItemCollection = new ContentItemCollection();
             _contentItemCollection.Load(packageAssets);
 
-            PackageAssets = _contentItemCollection.FindItems(_conventions.Patterns.AnyTargettedFile);
-            RefAssets = _contentItemCollection.FindItems(_conventions.Patterns.CompileRefAssemblies);
-            LibAssets = _contentItemCollection.FindItems(_conventions.Patterns.CompileLibAssemblies);
+            PackageAssets = GetContentItemsFromPattern(_conventions.Patterns.AnyTargettedFile);
+            RefAssets = GetContentItemsFromPattern(_conventions.Patterns.CompileRefAssemblies);
+            LibAssets = GetContentItemsFromPattern(_conventions.Patterns.CompileLibAssemblies);
             CompileAssets = RefAssets.Any() ? RefAssets : LibAssets;
-            RuntimeAssets = _contentItemCollection.FindItems(_conventions.Patterns.RuntimeAssemblies);
+            RuntimeAssets = GetContentItemsFromPattern(_conventions.Patterns.RuntimeAssemblies);
             RuntimeSpecificAssets = RuntimeAssets.Where(t => t.Path.StartsWith("runtimes")).ToArray();
             Rids = RuntimeSpecificAssets.Select(t => (string)t.Properties["rid"])
                 .Distinct()
@@ -108,6 +108,13 @@ public Package(string packagePath,
                 .Distinct()
                 .ToArray();
             AssemblyReferences = assemblyReferences;
+
+            IEnumerable<ContentItem> GetContentItemsFromPattern(PatternSet pattern)
+            {
+                List<ContentItemGroup> itemGroups = new();
+                _contentItemCollection.PopulateItemGroups(pattern, itemGroups);
+                return itemGroups.SelectMany(i => i.Items).ToArray();
+            }
         }
 
         public static void InitializeRuntimeGraph(string runtimeGraph)