[Work Item]: GCA don't allow generic anon consts

[BoxyUwU]

these can now just be paths to normal const items

currently this compiles:

#![feature(generic_const_args, min_generic_const_args, generic_const_items)]

type const FOO<const N: usize>: usize = const { N + 1 };

but we should go back to rejecting this now that people can just write const FOO<const N: usize>: usize = N + 1; and then use FOO<N> in the type system even though it's not a type const

This issue has been assigned to @LaneAsade via this comment.

[BoxyUwU]

@rustbot assign @LaneAsade