Build ServiceDiscovery library and tests against .NET Framework

This enables scenarios to use the library on .NET Framework. This is mostly done by using C# 14 new extension syntax so very little code changes were made but rather the APIs that didn't exist are added into FrameworkExtensions classes to light them up on .NET Core builds.

Author: twsouthwick

src/Microsoft.Extensions.ServiceDiscovery/Microsoft.Extensions.ServiceDiscovery.csproj

@@ -1,21 +1,27 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>$(DefaultTargetFramework)</TargetFramework>
+    <TargetFrameworks>$(DefaultTargetFramework);net462</TargetFrameworks>
     <IsPackable>true</IsPackable>
-    <IsAotCompatible>true</IsAotCompatible>
+    <IsAotCompatible Condition=" '$(TargetFramework)' != 'net462' ">true</IsAotCompatible>
     <Description>Provides extensions to HttpClient that enable service discovery based on configuration.</Description>
     <PackageIconFullPath>$(DefaultDotnetIconFullPath)</PackageIconFullPath>
   </PropertyGroup>
 
   <ItemGroup>
     <PackageReference Include="Microsoft.Extensions.Http" />
-    <InternalsVisibleTo Include="Microsoft.Extensions.ServiceDiscovery.Tests"/>
-    <InternalsVisibleTo Include="Microsoft.Extensions.ServiceDiscovery.Dns.Tests"/>
+    <InternalsVisibleTo Include="Microsoft.Extensions.ServiceDiscovery.Tests" />
+    <InternalsVisibleTo Include="Microsoft.Extensions.ServiceDiscovery.Dns.Tests" />
   </ItemGroup>
 
   <ItemGroup>
     <ProjectReference Include="..\Microsoft.Extensions.ServiceDiscovery.Abstractions\Microsoft.Extensions.ServiceDiscovery.Abstractions.csproj" />
   </ItemGroup>
 
+  <ItemGroup Condition=" '$(TargetFramework)' == 'net462' ">
+    <PackageReference Include="Microsoft.Bcl.TimeProvider" />
+  </ItemGroup>
+
+  <Import Project="$(SharedDir)FxPolyfills\FxPolyfills.targets" />
+
 </Project>

src/Microsoft.Extensions.ServiceDiscovery/ServiceDiscoveryHttpClientBuilderExtensions.cs

@@ -1,12 +1,15 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using Microsoft.Extensions.DependencyInjection.Extensions;
-using Microsoft.Extensions.Http;
 using Microsoft.Extensions.Options;
 using Microsoft.Extensions.ServiceDiscovery;
 using Microsoft.Extensions.ServiceDiscovery.Http;
 
+#if NET
+using Microsoft.Extensions.DependencyInjection.Extensions;
+using Microsoft.Extensions.Http;
+#endif
+
 namespace Microsoft.Extensions.DependencyInjection;
 
 /// <summary>
@@ -34,13 +37,15 @@ public static IHttpClientBuilder AddServiceDiscovery(this IHttpClientBuilder htt
             return new ResolvingHttpDelegatingHandler(registry, options);
         });
 
+#if NET
         // Configure the HttpClient to disable gRPC load balancing.
         // This is done on all HttpClient instances but only impacts gRPC clients.
         AddDisableGrpcLoadBalancingFilter(httpClientBuilder.Services, httpClientBuilder.Name);
-
+#endif
         return httpClientBuilder;
     }
 
+#if NET
     private static void AddDisableGrpcLoadBalancingFilter(IServiceCollection services, string? name)
     {
         // A filter is used because it will always run last. This is important because the disable
@@ -86,4 +91,5 @@ public Action<HttpMessageHandlerBuilder> Configure(Action<HttpMessageHandlerBuil
             };
         }
     }
+#endif
 }