Auto merge of #6046 - rail-rain:change_criteria_non_copy_const, r=flip1995
Change the criteria of `interior_mutable_const`
This implements my suggestion [here](https://github.com/rust-lang/rust-clippy/issues/5050#issuecomment-
680310889), and so hopefully fixes #5050.
* stop linting associated types and generic type parameters
* start linting ones in trait impls
whose corresponding definitions in the traits are generic
* remove the `is_copy` check
as presumably the only purpose of it is to allow
generics with `Copy` bounds as `Freeze` is internal
and generics are no longer linted
* remove the term 'copy' from the tests
as being `Copy` no longer have meaning
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changelog: Change the criteria of `declare_interior_mutable_const` and `borrow_interior_mutable_const` to narrow the lints to only lint things that defenitly is a interior mutable type, not potentially.