associated type_consts can have defaults without the `associated_type_defaults` feature gate

[BoxyUwU]

The following is valid rust code:

#![feature(min_generic_const_args)

trait Trait {
    #[type_const]`
    const ASSOC: usize = 10;
}

We don't allow this for types, e.g. type Assoc = u32;. I expect associated type consts to have equivalent problems to associated type defaults given they are functionally equivalent in the type system. We should feature gate this under associated_type_defaults

[LaneAsade]

@rustbot claim