[tools] Enable xml doc generation for dotnet-linker. (#24950)

This way we get validation of any xml docs in dotnet-linker.

Also make all warnings errors, since we're now warning-free.

Author: rolfbjarne

src/Foundation/ExportAttribute.cs

@@ -36,6 +36,7 @@
 
 namespace Foundation {
 
+#if !BUNDLER
 	/// <summary>Exports a method or property to the Objective-C world.</summary>
 	///     <remarks>
 	///       <para>
@@ -52,6 +53,7 @@ namespace Foundation {
 	///   ]]></code>
 	///       </example>
 	///     </remarks>
+#endif
 	[AttributeUsage (AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Property)]
 	public class ExportAttribute : Attribute {
 		string? selector;

tools/common/StringUtils.cs

@@ -247,7 +247,7 @@ public static Version ParseVersion (string v)
 		/// <param name="code">The code of the message.</param>
 		/// <param name="message">The message text.</param>
 		/// <returns></returns>
-		/// <see cref="https://learn.microsoft.com/visualstudio/msbuild/msbuild-diagnostic-format-for-tasks"/>
+		/// <see href="https://learn.microsoft.com/visualstudio/msbuild/msbuild-diagnostic-format-for-tasks"/>
 		public static string FormatMessage (string? fileName, long? lineNumber, bool isError, string prefix, int code, string message)
 		{
 			var sb = new StringBuilder ();

tools/dotnet-linker/dotnet-linker.csproj

@@ -4,9 +4,11 @@
     <RootNamespace>dotnet_linker</RootNamespace>
     <DefineConstants>$(DefineConstants);BUNDLER</DefineConstants>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
-    <WarningsAsErrors>nullable</WarningsAsErrors>
+    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <AppendTargetFrameworkToOutputPath>false</AppendTargetFrameworkToOutputPath>
     <Nullable>enable</Nullable>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <NoWarn>$(NoWarn);CS1591</NoWarn> <!-- Missing XML comment for publicly visible type or member: don't care, the APIs aren't for public consumption -->
   </PropertyGroup>
 
   <Import Project="..\..\eng\Versions.props" />