Translate PlaceholderParser::apply_config to C++.

xs/src/PlaceholderParser.hpp

@@ -5,6 +5,7 @@
 #include <myinit.h>
 #include <map>
 #include <string>
+#include "PrintConfig.hpp"
 
 
 namespace Slic3r {
@@ -17,6 +18,13 @@ class PlaceholderParser
 
     PlaceholderParser();
     ~PlaceholderParser();
+
+    void apply_config(DynamicPrintConfig &config);
+
+    private:
+    template<class T>
+    void set_multiple_from_vector(
+        const std::string &key, ConfigOptionVector<T> &opt);
 };
 
 }