Warn when direct package reference is unused

Repro for #119

Author: stan-sz

src/Tests/E2ETests.cs

@@ -314,6 +314,17 @@ public Task UnusedPackageReference()
             });
     }
 
+    [TestMethod]
+    public Task UnusedPackageReferenceWithSdk()
+    {
+        return RunMSBuildAsync(
+            projectFile: "Test/Test.csproj",
+            expectedWarnings:
+            [
+                new Warning("RT0003: PackageReference Moq can be removed", "Test/Test.csproj")
+            ]);
+    }
+
     [TestMethod]
     public Task UnusedPackageReferenceNoWarn()
     {

src/Tests/TestData/UnusedPackageReferenceWithSdk/Test/Test.cs

@@ -0,0 +1,9 @@
+using Castle.Core.Logging;
+
+namespace Test
+{
+    public class Foo
+    {
+        public static ILogger Logger() => NullLogger.Instance;
+    }
+}

src/Tests/TestData/UnusedPackageReferenceWithSdk/Test/Test.csproj

@@ -0,0 +1,12 @@
+<Project Sdk="MSTest.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>net8.0</TargetFramework>
+    <ExplicitUsings>enable</ExplicitUsings>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Moq" Version="4.20.72" />
+  </ItemGroup>
+
+</Project>