Use ahash for most HashMaps and HashSets

[kennethloeffler]

This PR replaces most HashMaps with AHashMap. I did it the lazy way with type aliases, didn't do anything to rbx_xml (yet?), and haven't touched the changelogs yet, because I am tired and I want to go to bed! It's kind of invasive, and might make the library harder to use, but we do get a nice performance boost from it.

On my machine, this improves rbx_binary's "Deserialize 10,000 Parts" and "Serialize 10,000 Parts" benchmarks by ~15% and ~19%, respectively.

[Dekkonot]

It's kind of invasive, and might make the library harder to use, but we do get a nice performance boost from it.

I do have some concerns about changing the reflection database to use AHashMap, since we aren't the only consumers. The only other public interface this would impact is WeakDom::into_raw though and I think it's probably fine to leak that. I don't know how many people are using that API but it's probably fine to slightly break it since we're already making a breaking change anyway.

This will impact Argon and Rojo, but those are the only ones I can think of off the top of my head. They'll already have to do a bunch of changes to update to rbx_weak_dom 3.0 though, so it's probably fine.

[kennethloeffler]

After some further benchmarking, using ahash in rbx_reflection is a bit of a wash. It didn't effect rbx_binary's deserialization performance at all, and if anything made rbx_binary's serialization performance worse. Good for me, fewer changelogs to touch :D