[mono] Fixed getting namespace names of array types. (#80426)

* [mono] Fixed getting namespace names of array types. #42633

* [mono] Namespace getter icall of Type, code style.

* Reenabled TypeInfoTests.Namespace for Mono.

* [mono] Namespace for array types now works also for jagged arrays.

* [mono] Fixed Type.Namespace for enums.

* [mono] Fixed failing Microsoft.XmlSerializer.Generator.Tests.SgenCommandTest.

* Adding cases to TypeInfoTests.Namespace test.

src/libraries/System.Reflection/tests/TypeInfoTests.cs

@@ -1474,7 +1474,8 @@ public void IsVisible(Type type, bool expected)
         [InlineData(typeof(int), "System")]
         [InlineData(typeof(TI_BaseClass[]), "System.Reflection.Tests")]
         [InlineData(typeof(TI_BaseClass.PublicNestedClass1[]), "System.Reflection.Tests")]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/42633", TestRuntimes.Mono)]
+        [InlineData(typeof(TI_BaseClass.PublicNestedClass1[][]), "System.Reflection.Tests")]
+        [InlineData(typeof(TI_Struct*), "System.Reflection.Tests")]
         public void Namespace(Type type, string expected)
         {
             Assert.Equal(expected, type.GetTypeInfo().Namespace);
@@ -1864,6 +1865,10 @@ public class ClassWithExplicitStructLayout
             public short y;
         }
     }
+    public struct TI_Struct
+    {
+        public int _field;
+    }
     public class TI_BaseClass
     {
         static TI_BaseClass() { }

src/mono/mono/metadata/icall.c

@@ -2988,6 +2988,12 @@ ves_icall_RuntimeType_GetNamespace (MonoQCallTypeHandle type_handle, MonoObjectH
 {
 	MonoType *type = type_handle.type;
 	MonoClass *klass = mono_class_from_mono_type_internal (type);
+
+	MonoClass *elem;
+	while (!m_class_is_enumtype (klass) && 
+		!mono_class_is_nullable (klass) &&
+		(klass != (elem = m_class_get_element_class (klass))))
+		klass = elem;
 
 	MonoClass *klass_nested_in;
 	while ((klass_nested_in = m_class_get_nested_in (klass)))