Add feature switch to control HTTP3 support (#49564)

Author: MichalStrehovsky

src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.targets

@@ -623,6 +623,11 @@ Copyright (c) .NET Foundation. All rights reserved.
                                     Value="$(_UseManagedNtlm)"
                                     Trim="true" />
 
+    <RuntimeHostConfigurationOption Include="System.Net.SocketsHttpHandler.Http3Support"
+                                    Condition="'$(Http3Support)' != ''"
+                                    Value="$(Http3Support)"
+                                    Trim="true" />
+
     <RuntimeHostConfigurationOption Include="System.Reflection.Metadata.MetadataUpdater.IsSupported"
                                     Condition="'$(MetadataUpdaterSupport)' != ''"
                                     Value="$(MetadataUpdaterSupport)"

test/Microsoft.NET.Publish.Tests/GivenThatWeWantToPublishAProjectWithAllFeatures.cs

@@ -80,6 +80,7 @@ public void It_publishes_the_project_correctly(string targetFramework, string[]
             ""System.Net.Http.EnableActivityPropagation"": false,
             ""System.Net.Http.UseNativeHttpHandler"": true,
             ""System.Net.Security.UseManagedNtlm"": true,
+            ""System.Net.SocketsHttpHandler.Http3Support"": false,
             ""System.Reflection.Metadata.MetadataUpdater.IsSupported"": false,
             ""System.Reflection.NullabilityInfoContext.IsSupported"": false,
             ""System.Resources.ResourceManager.AllowCustomResourceTypes"": false,

test/TestAssets/TestProjects/KitchenSink/TestApp/TestApp.csproj

@@ -30,6 +30,7 @@
     <HttpActivityPropagationSupport>false</HttpActivityPropagationSupport>
     <UseNativeHttpHandler>true</UseNativeHttpHandler>
     <_UseManagedNtlm>true</_UseManagedNtlm>
+    <Http3Support>false</Http3Support>
     <MetadataUpdaterSupport>false</MetadataUpdaterSupport>
     <NullabilityInfoContextSupport>false</NullabilityInfoContextSupport>
     <CustomResourceTypesSupport>false</CustomResourceTypesSupport>