MGCA: uses of type_const items inside of bodies should lower to `mir::Const::Ty`

[BoxyUwU]

Currently using a type_const item in a body will result in ICEs (playground):

#![feature(min_generic_const_args)]

#[type_const]
const CONST: usize = 1;

fn uses_const() {
   CONST;
}

This is caused by treating them as "normal" uses of const items which have bodies and then trying to evaluate them. Instead we should lower them as consts coming from the type system (mir::Const::Ty) so that they will be handled by type system normalization which can properly process them.

cc @camelid I've assigned you since we briefly talked about this but I don't think you ever actually agreed to work on this. Just unassign yourself if you don't wanna work on it :)

[dharmvr1]

hey @BoxyUwU @camelid , i am actually reading about mir and compiler from so long but did not get any good first issue if this possible , can u please assign it to me , love to work on it

[camelid]

Hi @dharmvr1, you can use @rustbot claim if you want to work on this issue.

[dharmvr1]

@rustbot claim