Optimize Node::add_child validation

Adding 10k nodes is almost twice as fast.

core/string/ustring.cpp

@@ -2593,6 +2593,23 @@ double String::to_float(const wchar_t *p_str, const wchar_t **r_end) {
 	return built_in_strtod<wchar_t>(p_str, (wchar_t **)r_end);
 }
 
+uint32_t String::num_characters(int64_t p_int) {
+	int r = 1;
+	if (p_int < 0) {
+		r += 1;
+		if (p_int == INT64_MIN) {
+			p_int = INT64_MAX;
+		} else {
+			p_int = -p_int;
+		}
+	}
+	while (p_int >= 10) {
+		p_int /= 10;
+		r++;
+	}
+	return r;
+}
+
 int64_t String::to_int(const char32_t *p_str, int p_len, bool p_clamp) {
 	if (p_len == 0 || !p_str[0]) {
 		return 0;
@@ -4561,15 +4578,65 @@ String String::property_name_encode() const {
 }
 
 // Changes made to the set of invalid characters must also be reflected in the String documentation.
-const String String::invalid_node_name_characters = ". : @ / \" " UNIQUE_NODE_PREFIX;
+
+static const char32_t invalid_node_name_characters[] = { '.', ':', '@', '/', '\"', UNIQUE_NODE_PREFIX[0], 0 };
+
+String String::get_invalid_node_name_characters() {
+	// Do not use this function for critical validation.
+	String r;
+	const char32_t *c = invalid_node_name_characters;
+	while (*c) {
+		if (c != invalid_node_name_characters) {
+			r += " ";
+		}
+		r += String::chr(*c);
+		c++;
+	}
+	return r;
+}
 
 String String::validate_node_name() const {
-	Vector<String> chars = String::invalid_node_name_characters.split(" ");
-	String name = this->replace(chars[0], "");
-	for (int i = 1; i < chars.size(); i++) {
-		name = name.replace(chars[i], "");
+	// This is a critical validation in node addition, so it must be optimized.
+	const char32_t *cn = ptr();
+	if (cn == nullptr) {
+		return String();
 	}
-	return name;
+	bool valid = true;
+	uint32_t idx = 0;
+	while (cn[idx]) {
+		const char32_t *c = invalid_node_name_characters;
+		while (*c) {
+			if (cn[idx] == *c) {
+				valid = false;
+				break;
+			}
+			c++;
+		}
+		if (!valid) {
+			break;
+		}
+		idx++;
+	}
+
+	if (valid) {
+		return *this;
+	}
+
+	String validated = *this;
+	char32_t *nn = validated.ptrw();
+	while (nn[idx]) {
+		const char32_t *c = invalid_node_name_characters;
+		while (*c) {
+			if (nn[idx] == *c) {
+				nn[idx] = '_';
+				break;
+			}
+			c++;
+		}
+		idx++;
+	}
+
+	return validated;
 }
 
 String String::get_basename() const {