ArgsParser: Add support for Optional<size_t>

Userland/Libraries/LibCore/ArgsParser.cpp

@@ -484,6 +484,22 @@ void ArgsParser::add_option(Optional<double>& value, const char* help_string, co
     add_option(move(option));
 }
 
+void ArgsParser::add_option(Optional<size_t>& value, const char* help_string, const char* long_name, char short_name, const char* value_name)
+{
+    Option option {
+        true,
+        help_string,
+        long_name,
+        short_name,
+        value_name,
+        [&value](const char* s) {
+            value = AK::StringUtils::convert_to_uint<size_t>(s);
+            return value.has_value();
+        }
+    };
+    add_option(move(option));
+}
+
 void ArgsParser::add_positional_argument(Arg&& arg)
 {
     m_positional_args.append(move(arg));

Userland/Libraries/LibCore/ArgsParser.h

@@ -78,6 +78,7 @@ public:
     void add_option(unsigned& value, const char* help_string, const char* long_name, char short_name, const char* value_name);
     void add_option(double& value, const char* help_string, const char* long_name, char short_name, const char* value_name);
     void add_option(Optional<double>& value, const char* help_string, const char* long_name, char short_name, const char* value_name);
+    void add_option(Optional<size_t>& value, const char* help_string, const char* long_name, char short_name, const char* value_name);
 
     void add_positional_argument(Arg&&);
     void add_positional_argument(const char*& value, const char* help_string, const char* name, Required required = Required::Yes);