64-bit DLL (and a less ancient extension system)

The inputs/outputs of the system haven’t changed, but:

• Built a 64-bit version of the DLL; there’s still a 32-bit version for compatibility if you really want it, but there’s honestly no reason to write 32-bit software in 2022 so I hope nobody does
• Extension is connected to GameMaker using the new (and by “new” I mean we’ve had it for at least five years) extension mechanism, rather than the external_define that’s been here since like GameMaker 6

Not 100% sure why I didn’t do this the first time around. I probably forgot about them, honestly.