LibJS: Make Function and CallFrame aware of their function name

Author: https://github.com/linusg
Commit: eece424694
Pull-request: https://github.com/SerenityOS/serenity/pull/1742

Libraries/LibJS/Runtime/Function.h

@@ -37,6 +37,7 @@ public:
 
     virtual Value call(Interpreter&) = 0;
     virtual Value construct(Interpreter&) = 0;
+    virtual const FlyString& name() const = 0;
 
 protected:
     Function();