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

Yes I’ve been spending a bit of time looking at my old extensions and making them 64-bit, what of it?

• 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

This one, unlike Sprite Atlas from earlier today, at least has the excuse that I made it months before 64-bit GameMaker was really a thing, and I don’t think I’ve looked at the code since then.