Short-circuit recursive ResolveInterfaceMethodToVirtualMethodOnType

When ResolveInterfaceMethodToVirtualMethodOnType is recursively calling
itself, use the result instead of returning `null` and then continuing
the outer loop that is effectively doing the same recursion on base
types.

Author: filipnavara

src/coreclr/tools/Common/TypeSystem/Common/MetadataVirtualMethodAlgorithm.cs

@@ -610,7 +610,7 @@ public override MethodDesc ResolveVariantInterfaceMethodToStaticVirtualMethodOnT
         //    function returns null if the interface method implementation is not defined by the current type in
         //    the hierarchy.For variance to work correctly, this requires that interfaces be queried in correct order.
         //    See current interface call resolution for details on how that happens.
-        private static MethodDesc ResolveInterfaceMethodToVirtualMethodOnType(MethodDesc interfaceMethod, MetadataType currentType)
+        private static MethodDesc ResolveInterfaceMethodToVirtualMethodOnType(MethodDesc interfaceMethod, MetadataType currentType, bool returnRecursive = false)
         {
             Debug.Assert(!interfaceMethod.Signature.IsStatic);
 
@@ -665,7 +665,7 @@ private static MethodDesc ResolveInterfaceMethodToVirtualMethodOnType(MethodDesc
                 MethodDesc baseClassImplementationOfInterfaceMethod = ResolveInterfaceMethodToVirtualMethodOnTypeRecursive(interfaceMethod, baseType);
                 if (baseClassImplementationOfInterfaceMethod != null)
                 {
-                    return null;
+                    return returnRecursive ? baseClassImplementationOfInterfaceMethod : null;
                 }
                 else
                 {
@@ -716,6 +716,7 @@ public static MethodDesc ResolveVariantInterfaceMethodToVirtualMethodOnType(Meth
         // Helper routine used during implicit interface implementation discovery
         private static MethodDesc ResolveInterfaceMethodToVirtualMethodOnTypeRecursive(MethodDesc interfaceMethod, MetadataType currentType)
         {
+            MethodDesc savedResult = null;
             while (true)
             {
                 if (currentType == null)
@@ -729,7 +730,7 @@ private static MethodDesc ResolveInterfaceMethodToVirtualMethodOnTypeRecursive(M
                     return null;
                 }
 
-                MethodDesc currentTypeInterfaceResolution = ResolveInterfaceMethodToVirtualMethodOnType(interfaceMethod, currentType);
+                MethodDesc currentTypeInterfaceResolution = ResolveInterfaceMethodToVirtualMethodOnType(interfaceMethod, currentType, returnRecursive: true);
                 if (currentTypeInterfaceResolution != null)
                     return currentTypeInterfaceResolution;