Support for UWP .NET Native even if devs modified their Default.rd.xml (#3703)

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## Fixes #3093
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Fixing niche case where UWP devs modified their Default.rd.xml causing the library to not work in .NET Native. Thanks to https://github.com/OfficeDev/Open-XML-SDK/pull/241/files used that as reference!

## PR Type
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 - Bugfix
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## What is the current behavior?
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See issue

## What is the new behavior?
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It works!

## PR Checklist

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## Other information

Author: msftbot[bot]

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

@@ -35,6 +35,11 @@
     <PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform" Version="$(ExtrasUwpMetaPackageVersion)" PrivateAssets="all" IsImplicitlyDefined="true" />
   </ItemGroup>
 
+  <!-- In order to support .NET Native, we need to include an appropriate .rd.xml for UWP (remove from everything else) -->
+  <ItemGroup Condition="'$(TargetFramework)' != 'uap10.0.19041' and '$(TargetFramework)' != 'native'">
+    <EmbeddedResource Remove="Properties\Microsoft.Toolkit.Uwp.Notifications.rd.xml" />
+  </ItemGroup>
+
   <ItemGroup>
     <None Include="Microsoft.Toolkit.Uwp.Notifications.targets" Pack="true" PackagePath="build\native" />
   </ItemGroup>

Microsoft.Toolkit.Uwp.Notifications/Properties/Microsoft.Toolkit.Uwp.Notifications.rd.xml

@@ -0,0 +1,13 @@
+<!--
+    This file enable reflections for Toolkit.Notifications and all of its public/private members,
+    enabling the library to work in .NET Native even if developers modified their default rd.xml.
+    See issue https://github.com/windows-toolkit/WindowsCommunityToolkit/issues/3093 for more details.
+-->
+
+<Directives xmlns="http://schemas.microsoft.com/netfx/2013/01/metadata">
+  <Library Name="Microsoft.Toolkit.Uwp.Notifications">
+    <!-- TODO: We can potentially minimize the metadata needed, but further
+         investigation is needed to fill this in and adequately test this -->
+    <Assembly Name="Microsoft.Toolkit.Uwp.Notifications" Dynamic="Required All" />
+  </Library>
+</Directives>