Add Support for Modifier-Based Combo Keybinds

Allow players to bind actions to key combinations by assigning any key as a custom modifier. For example, pressing U could toggle the flashlight, while Right Alt + U could toggle the laser. Similarly, R could reload the weapon, while Right Alt + R could check the magazine. This would allow multiple related actions to share the same primary key, reducing the number of separate buttons players need to remember. It would make complex controls more flexible, intuitive, and accessible for players using custom layouts or devices with fewer available inputs.