Allow passing IntPtr values with UnmanagedType.AsAny. (dotnet#2039)

This is used by the SplashScreen class of WindowsBase in .NET Core to pass a NULL pointer.

Co-authored-by: Vincent Povirk <[email protected]>

src/mono/mono/metadata/marshal.c

@@ -6210,6 +6210,7 @@ mono_marshal_asany_impl (MonoObjectHandle o, MonoMarshalNative string_encoding,
 	case MONO_TYPE_I4:
 	case MONO_TYPE_U4:
 	case MONO_TYPE_PTR:
+	case MONO_TYPE_I:
 	case MONO_TYPE_I1:
 	case MONO_TYPE_U1:
 	case MONO_TYPE_BOOLEAN:

src/mono/mono/tests/libtest.c

@@ -1834,6 +1834,9 @@ mono_test_asany (void *ptr, int what)
 			return 1;
 		}
 	}
+	case 5: {
+		return (*(intptr_t*)ptr == 5) ? 0 : 1;
+	}
 	default:
 		g_assert_not_reached ();
 	}

src/mono/mono/tests/pinvoke2.cs

@@ -1088,6 +1088,9 @@ public static int test_0_asany () {
 		catch (ArgumentException) {
 		}
 
+		if (mono_test_asany (new IntPtr(5), 5) != 0)
+			return 7;
+
 		return 0;
 	}