`impl const B` only needs `impl A` for `trait B: A`

[fee1-dead]

From #86571 (comment).

I tried this code (playground):

#![feature(const_trait_impl)]
trait A {}
trait B: A {}

struct Foo;

impl A for Foo {}
impl const B for Foo {}

I expected to see this happen: The compiler might error because Foo does not impl const A

Instead, this happened: This code has no compiler errors.

This is for discussion. I am neither for nor against how this is handled currently.

@rustbot label requires-nightly F-const_trait_impl