Fix interface trimming order (#110098)

ProcessMarkedTypesWithInterfaces can lead to additional interface
methods being required, so those need to be marked (done by
ProcessInterfaceMethods) even if nothing else happens to put new items
in the queue.

Author: sbomer

src/tools/illink/src/linker/Linker.Steps/MarkStep.cs

@@ -415,8 +415,8 @@ bool ProcessPrimaryQueue ()
 
 			while (!QueueIsEmpty ()) {
 				ProcessQueue ();
-				ProcessInterfaceMethods ();
 				ProcessMarkedTypesWithInterfaces ();
+				ProcessInterfaceMethods ();
 				ProcessDynamicCastableImplementationInterfaces ();
 				ProcessPendingBodies ();
 				DoAdditionalProcessing ();

src/tools/illink/test/Mono.Linker.Tests.Cases/Attributes/OnlyKeepUsed/MethodWithUnmanagedConstraint.cs

@@ -6,6 +6,11 @@ namespace Mono.Linker.Tests.Cases.Attributes.OnlyKeepUsed
 {
 	[SetupCSharpCompilerToUse ("csc")]
 	[SetupLinkerArgument ("--used-attrs-only", "true")]
+
+	// Necessary to allow trimming the attribute instance from types in CoreLib.
+	[SetupLinkerTrimMode ("link")]
+	// When we allow trimming CoreLib, some well-known types expected by ILVerify are removed.
+	[SkipILVerify]
 	public class MethodWithUnmanagedConstraint
 	{
 		public static void Main ()