normalize slashes and casing when comparing includes

src/dotnet/MsbuildProjectExtensions.cs

@@ -66,7 +66,16 @@ namespace Microsoft.DotNet.Tools
 
         public static bool HasInclude(this ProjectItemElement el, string include)
         {
-            return el.Includes().Contains(include);
+            include = NormalizeIncludeForComparison(include);
+            foreach (var i in el.Includes())
+            {
+                if (include == NormalizeIncludeForComparison(i))
+                {
+                    return true;
+                }
+            }
+
+            return false;
         }
 
         private static bool TryGetFrameworkConditionString(string framework, out string condition)
@@ -80,5 +89,10 @@ namespace Microsoft.DotNet.Tools
             condition = $"'$(TargetFramework)' == '{framework}'";
             return true;
         }
+
+        private static string NormalizeIncludeForComparison(string include)
+        {
+            return P2PHelpers.NormalizeSlashesForMsbuild(include.ToLower());
+        }
     }
 }

src/dotnet/commands/dotnet-add-p2p/Program.cs

@@ -3,10 +3,7 @@
 
 using Microsoft.DotNet.Cli.CommandLine;
 using Microsoft.DotNet.Cli.Utils;
-using Microsoft.Build.Construction;
-using Microsoft.DotNet.Tools.Common;
 using System.Collections.Generic;
-using System.IO;
 
 namespace Microsoft.DotNet.Tools.Add.ProjectToProjectReference
 {

src/dotnet/commands/dotnet-remove-p2p/Program.cs

@@ -3,10 +3,7 @@
 
 using Microsoft.DotNet.Cli.CommandLine;
 using Microsoft.DotNet.Cli.Utils;
-using Microsoft.Build.Construction;
-using Microsoft.DotNet.Tools.Common;
 using System.Collections.Generic;
-using System.IO;
 
 namespace Microsoft.DotNet.Tools.Remove.ProjectToProjectReference
 {