Add the ability to make Java version-specific command-line arguments

As far as I'm aware, the only thing preventing Minecraft Forge from supporting Java 16 is the inability to specify the command-line argument `--illegal-access=permit`. Because the flag was first introduced in Java 9, specifying it causes any clients running on Java 8 or lower to crash instantly, but not specifying it prevents Forge or other mods from properly utilizing reflection.