[mono][metadata] Fix overriding of methods from parent variant interf…

…aces

As an example from the now enabled test.

```
interface InterfaceScenario2<in T> {
	static abstract int Method ();
}

class BaseScenario2 : InterfaceScenario2<string, InterfaceScenario2<object> {
	public static int Method() {
//		.override method int32 class InterfaceScenario2`1<string>::Method()
		return 2;
	}

	public static int32 Method_Obj() {
//		.override method int32 class InterfaceScenario2`1<object>::Method()
		return 3;
	}
}

class DerivedScenario2 : BaseScenario2 {
	public static int Method () {
//		.override method int32 class InterfaceScenario2`1<object>::Method()
		return 6;
	}
}

public static string Test_Scenario2_1<T, ImplType>() where ImplType : InterfaceScenario2<T> {
	return ImplType.Method ().ToString ();
}

Test_Scenario2_1<string, DerivedScenario2> ());
```

This test calls InterfaceScenario2<string> on DerviedScenario2. This should call DerivedScenario2.Method (not BaseScenario2.Method) because this method overrides (in BaseScenario2) both the obvious slot for InterfaceScenario2<object> as well as the slot for variant compatible interface InterfaceScenario2<string>.

src/mono/mono/metadata/class-setup-vtable.c

@@ -1035,6 +1035,37 @@ apply_override (MonoClass *klass, MonoClass *override_class, MonoMethod **vtable
 	return TRUE;
 }
 
+/*
+ * Interface method `decl` is overridden in `klass` with `override`. In addition to overriding the method slot
+ * for this interface method, if parent klass implements a different variant compatible interface, then we also
+ * need to override the correpsonding method slot in this other interface.
+ */
+static void
+apply_override_variant_interface (MonoClass *klass, MonoMethod *decl, MonoMethod *override, MonoMethod **vtable)
+{
+	MonoClass *parent = klass->parent;
+
+	// This handles variant overrides for static virtual methods only
+	if (!m_method_is_static (decl))
+		return;
+
+	if (mono_class_has_variant_generic_params (decl->klass) && parent) {
+		for (int k = 0; k < klass->parent->interface_offsets_count; k++) {
+			MonoClass *impl_itf = parent->interfaces_packed [k];
+			if (decl->klass != impl_itf &&
+					mono_class_has_variant_generic_params (impl_itf) &&
+					mono_class_get_generic_type_definition (impl_itf) == mono_class_get_generic_type_definition (decl->klass)) {
+				if (mono_class_is_variant_compatible (impl_itf, decl->klass, FALSE)) {
+					int vt_slot = parent->interface_offsets_packed [k] + decl->slot;
+					vtable [vt_slot] = override;
+					TRACE_INTERFACE_VTABLE (printf ("\tvariance override slot %d with method %s\n", vt_slot, mono_method_full_name (override, TRUE)));
+					break;
+				}
+			}
+		}
+	}
+}
+
 static void
 handle_dim_conflicts (MonoMethod **vtable, MonoClass *klass, GHashTable *conflict_map)
 {
@@ -1788,6 +1819,7 @@ mono_class_setup_vtable_general (MonoClass *klass, MonoMethod **overrides, int o
 			g_assert (override->klass == klass);
 			if (!apply_override (klass, klass, vtable, decl, override, &override_map, &override_class_map, &conflict_map))
 				goto fail;
+			apply_override_variant_interface (klass, decl, override, vtable);
 		}
 	}
 

src/tests/issues.targets

@@ -1294,9 +1294,6 @@
         <ExcludeList Include="$(XunitTestBinBase)/Loader/classloader/StaticVirtualMethods/DiamondShape/**">
             <Issue>https://github.com/dotnet/runtime/issues/80350</Issue>
         </ExcludeList>
-        <ExcludeList Include="$(XunitTestBinBase)/Loader/classloader/StaticVirtualMethods/InterfaceVariance/**">
-            <Issue>Static virtual methods are not yet implemented in the Mono runtime.</Issue>
-        </ExcludeList>
         <ExcludeList Include="$(XunitTestBinBase)/Loader/classloader/StaticVirtualMethods/NegativeTestCases/**">
             <Issue>Static virtual methods are not yet implemented in the Mono runtime.</Issue>
         </ExcludeList>