std::string -> std::string_view

As per clang-tidy

Author: ehughsbaird

src/monstergenerator.cpp

@@ -824,7 +824,7 @@ struct special_attacks_reader : generic_typed_reader<special_attacks_reader> {
     }
 };
 
-void mtype::load( const JsonObject &jo, const std::string &src )
+void mtype::load( const JsonObject &jo, const std::string_view src )
 {
     MonsterGenerator &gen = MonsterGenerator::generator();
 

src/mtype.h

@@ -605,7 +605,7 @@ struct mtype {
         void faction_display( catacurses::window &w, const point &top_left, int width ) const;
 
         // Historically located in monstergenerator.cpp
-        void load( const JsonObject &jo, const std::string &src );
+        void load( const JsonObject &jo, std::string_view src );
 };
 
 #endif // CATA_SRC_MTYPE_H