Add an API to check if a Ty implements a trait

[momvart]

It can be handy to have an API that checks if a type implements a trait to not. Basic use cases include checking if the type implements some of the language-built-in marker traits like Copy.
The API can be added to Ty as follows.

fn implements(&self, def: TraitDef, generics: GenericArgs, param_env: ???) -> bool;

[momvart]

I think the implementation is straightforward using InferCtxt and type_implements_trait.

Anyway, I'm not sure how parameter environments are currently handled in smir.