Fixes #3012 working around NuGet/Home#8388

Tested with VS 2019 16.5 Preview 1

Author: michael-hawker

Microsoft.Toolkit.Uwp.Notifications/Microsoft.Toolkit.Uwp.Notifications.csproj

@@ -44,7 +44,9 @@
   <PropertyGroup Condition="'$(TargetFramework)' == 'native'">
     <OutputType>winmdobj</OutputType>
     <TargetPlatformIdentifier>UAP</TargetPlatformIdentifier>
-    <NugetTargetMoniker>UAP,Version=v10.0</NugetTargetMoniker>
+    <!-- Workaround for issue NuGet/Home#8388; change behavior during NuGet restore time vs. final build to avoid NuGet conflict in VS 2019 -->
+    <NugetTargetMoniker Condition="'$(DesignTimeBuild)' == 'true'">native</NugetTargetMoniker>
+    <NugetTargetMoniker Condition="'$(DesignTimeBuild)' != 'true'">UAP,Version=v10.0</NugetTargetMoniker>
     <PackageTargetFallback>uap10.0</PackageTargetFallback>
     <TargetPlatformVersion Condition="'$(TargetPlatformVersion)' == '' ">10.0.17763.0</TargetPlatformVersion>
     <TargetPlatformMinVersion Condition="'$(TargetPlatformMinVersion)' == '' ">10.0.10240.0</TargetPlatformMinVersion>