Add a way to setup an ArResolver

[expenses]

This is still very much a draft and builds ontop of #1, but it's usable enough to get an ArResolver working, see https://github.com/expenses/usd-iroh-resolver/tree/main.

This requires compiling a cdylib and using the ctor macro to declare a type and setup the factory:

https://github.com/expenses/usd-iroh-resolver/blob/cc5303975fe084ffd7d3b6dfd8965a13621b2d44/src/lib.rs#L317-L332

One thing that should be fixed before merging is that functions are currently passed as void *s. This is not ideal but babble isn't able to parse function pointers yet.

[anderslanglands]

Ooooh I see what you're doing. That's neat. I'd done something very similar with the bbl::Superclass<C> stuff in 0.6, but I was stymied in USD on the factory/type creation part. Very neat solution. In my case I was trying to attack a custom file format first. I'll have to see if I can do the same thing there and then hopefully we can generalize this approach.

[expenses]

In my case I was trying to attack a custom file format first. I'll have to see if I can do the same thing there and then hopefully we can generalize this approach.

Yep, I'l also interested in custom file formats. I believe that the exact same approach should work.