Fix build issues

Microsoft.Toolkit.Sample.Wpf.App/Microsoft.Toolkit.Sample.Wpf.App.csproj

@@ -3,7 +3,6 @@
     <ProjectGuid>{45524ED2-8B5A-42E8-97A2-DCA44ECC83AA}</ProjectGuid>
     <OutputType>WinExe</OutputType>
     <TargetFrameworks>net462;netcoreapp3.0</TargetFrameworks>
-    <AssetTargetFallback>uap10.0.18362</AssetTargetFallback>
     <Platforms>x86;x64</Platforms>
     <ProjectTypeGuids>{60dc8134-eba5-43b8-bcc9-bb4bc16c2548};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
     <AutoGenerateBindingRedirects>true</AutoGenerateBindingRedirects>

Microsoft.WinRT.Win32.targets

@@ -1,8 +1,13 @@
 <?xml version="1.0" encoding="utf-8" ?>
 <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
 
+  <PropertyGroup>
+    <DefaultTargetPlatformVersion Condition="'$(DefaultTargetPlatformVersion)'==''">18362</DefaultTargetPlatformVersion>
+    <AssetTargetFallback>uap10.0.$(DefaultTargetPlatformVersion)</AssetTargetFallback>
+  </PropertyGroup>
+
   <PropertyGroup Condition="'$(IntDir)'==''">
-    <IntDir>$(BaseIntermediateOutputPath)</IntDir>
+    <IntDir>$(BaseIntermediateOutputPath)\$(Platform)\$(Configuration)\$(TargetFramework)\</IntDir>
   </PropertyGroup>
   <ItemGroup>
     <PackageReference Include="Microsoft.VCRTForwarders.140" Version="1.0.0-rc" />