Make generic types' PartialEq, Eq, Hash and Debug implementations more flexible

[madsmtm]

We should consider implementing PartialEq, Eq, Hash and Debug on generic collections for all T: Message, instead of T: $trait + Message as is currently done via. #[derive].

Notes:

• Swift doesn't enable generics for NSArray, so it is comparable even if it contains AnyObject. It will try to call isEqual: on the elements below it, and that will expectedly crash if the type doesn't implement an isEqual: method, just like it does if you try to use the built-in conversion operators.
• Swift allows e.g. NSCache<AnyObject, AnyObject> to be hashable and comparable, since that type just does pointer comparison.
• The user can convert NSArray<AnyObject> -> NSObject, and compare those.
• This is not a soundness issue, the question is where it lies on the correctness vs. convenience scale?

Related to #559, #562 and #267.