Add PolySharp to polyfill attributes

Author: Cheesebaron

src/Jeffijoe.MessageFormat/Jeffijoe.MessageFormat.csproj

@@ -11,6 +11,7 @@
   	<LangVersion>latest</LangVersion>
   	<Nullable>enable</Nullable>
   	<TargetFrameworks>net6.0;net8.0;netstandard2.0;netstandard2.1</TargetFrameworks>
+    <PolySharpIncludeRuntimeSupportedAttributes>true</PolySharpIncludeRuntimeSupportedAttributes>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|AnyCPU'">
@@ -23,6 +24,10 @@
       <PrivateAssets>all</PrivateAssets>
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
     </PackageReference>
+    <PackageReference Include="PolySharp" Version="1.15.0">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
+    </PackageReference>
   </ItemGroup>
 
   <ItemGroup>