Construct remaining hot-path exceptions out of line so core functions inline (#5838)

* Construct remaining hot-path exceptions out of line so core functions inline

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Move throw_key_not_found() before at_impl()'s comment block

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

include/nlohmann/ordered_map.hpp

@@ -90,6 +90,15 @@ private:
         return self.end();
     }
 
+    /// @brief throw the exception of a failed at() lookup
+    /// @note kept out of line so that at_impl() stays small enough to inline
+    /// @throw std::out_of_range always
+    JSON_HEDLEY_NO_RETURN JSON_HEDLEY_NEVER_INLINE
+    static void throw_key_not_found()
+    {
+        JSON_THROW(std::out_of_range("key not found"));
+    }
+
     /// @brief shared implementation of the const and non-const at() overloads
     /// @throw std::out_of_range if @a key is not found
     template<typename Self, typename KeyType>
@@ -98,7 +107,7 @@ private:
         const auto it = find_impl(self, key);
         if (it == self.end())
         {
-            JSON_THROW(std::out_of_range("key not found"));
+            throw_key_not_found();
         }
         return it->second;
     }