LibJS: Add NativeFunction, a callable wrapper around a C++ lambda

This can be used to implement arbitrary functionality, callable from
JavaScript.

To make this work, I had to change the way CallExpression passes
arguments to the callee. Instead of a HashMap<String, Value>, we now
pass an ordered list of Argument { String name; Value value; }.

This patch includes a native "print(argument)" function. :^)

Libraries/LibJS/Makefile

@@ -6,6 +6,7 @@ OBJS = \
     HeapBlock.o \
     Interpreter.o \
     Lexer.o \
+    NativeFunction.o \
     Object.o \
     Parser.o \
     PrimitiveString.o \