Add `rafx-dynamic` feature/crate for dynamic linking about rafx HOT 2 CLOSED

This is the sort of thing I would expect to be done at an "engine" level - and I think there would be differing opinions on what exactly is wrapped/exposed, and the mechanics of doing the reload. If there's something in the crate that makes it particularly troublesome for someone to implement their own reloading we can consider making changes, but I don't think it's appropriate for this crate to force any particular approach on end users as this is an opinionated choice.

(That said, it may be worth profiling a compile that includes rafx and see if there is an obvious way we can reduce build times. There are some rust compile options that can help too. I think the bevy project might have some good material on this in their docs.)

from rafx.

Thanks, will look into profiling and there are cargo plugins which also can show which packages slow downs compilation in rafx and my program itself.

from rafx.