LibJS: Move ordinary_call_bind_this() to ECMAScriptFunctionObject

Now that it only needs to deal with ECMAScriptFunctionObject via
internal_call() / internal_construct(), we can:

- Remove the generic FunctionObject parameter
- Move it from the VM to ECMAScriptFunctionObject
- Make it private

Userland/Libraries/LibJS/Runtime/ECMAScriptFunctionObject.h

@@ -83,6 +83,7 @@ private:
     virtual void visit_edges(Visitor&) override;
 
     void prepare_for_ordinary_call(ExecutionContext& callee_context, Object* new_target);
+    void ordinary_call_bind_this(ExecutionContext&, Value this_argument);
     Completion ordinary_call_evaluate_body();
     ThrowCompletionOr<void> function_declaration_instantiation(Interpreter*);