10529: Generate `PartialOrd` implementations r=Veykril a=yoshuawuyts
_co-authored with `@rylev_`
This closes#5946 (which should've been closed already, lol). This PR makes it so we generate `PartialOrd` code implementations where possible. This is the last of Rust's built-in traits that was missing codegen.
After this has been merged we should look at moving the tests to a better spot, and maybe cleaning up the implementation somewhat (it's rather copy-pasty at the moment).
Either way, this finishes up the functionality. Thanks heaps!
Co-authored-by: Yoshua Wuyts <yoshuawuyts@gmail.com>