[Complex Test Layouts] Change String to use UTF-32 encoding on all platforms.

scene/main/node.cpp

@@ -1094,7 +1094,7 @@ String increase_numeric_string(const String &s) {
 		if (!carry) {
 			break;
 		}
-		CharType n = s[i];
+		char32_t n = s[i];
 		if (n == '9') { // keep carry as true: 9 + 1
 			res[i] = '0';
 		} else {
@@ -1155,7 +1155,7 @@ void Node::_generate_serial_child_name(const Node *p_child, StringName &name) co
 	String name_string = name;
 	String nums;
 	for (int i = name_string.length() - 1; i >= 0; i--) {
-		CharType n = name_string[i];
+		char32_t n = name_string[i];
 		if (n >= '0' && n <= '9') {
 			nums = String::chr(name_string[i]) + nums;
 		} else {