Question/request: const generic dependencies

(the adt_const_params tracking issue said to create an issue for questions and/or requests, so I'm doing that)

Under #![feature(adt_const_params)], I would expect the following to be allowed:

pub struct Array<const N: usize, const D: [usize; N]> {
    // ...
}

However, this gives an error:

error[E0770]: the type of const parameters must not depend on other generic parameters
  --> src/lib.rs:18:51
   |
18 | pub struct Array<const N: usize, const D: [usize; N]> {
   |                                                   ^ the type must not depend on the parameter `N`

This feels like a reasonably-common use of const type parameters; it would be nice for this to be supported.

Start by reproducing the adt_const_params example with const D: [usize; N] and inspect the reported E0770 diagnostic. Determine the language and compiler changes needed to permit const-parameter types that depend on earlier generic parameters; done means the example is accepted under the feature without regressing existing restrictions.