LibJS+LibWeb: Pass prototype to Object constructor

Everyone who constructs an Object must now pass a prototype object when
applicable. There's still a fair amount of code that passes something
fetched from the Interpreter, but this brings us closer to being able
to detach prototypes from Interpreter eventually.

Libraries/LibJS/Runtime/Function.cpp

@@ -30,8 +30,8 @@
 namespace JS {
 
 Function::Function(Object& prototype)
+    : Object(&prototype)
 {
-    set_prototype(&prototype);
 }
 
 Function::~Function()