Fix -[RLMSwiftCollectionBase isEqual:]

[lukaskollmer]

There is a bug in Realm where -[RLMSwiftCollectionBase isEqual:] does not correctly test for two List<>s equality.

Simple example:

class TestObject: RealmSwift.Object {
    let list = List<Int>()
}


let realm = try Realm()

let obj = TestObject()
obj.list.append(objectsIn: [1, 2, 3])

assert(obj.list == obj.list) // <- this will succeed (the list is currently still unmanaged)

try realm.write {
    realm.add(obj)
}

assert(obj.list == obj.list) // <- this will fail (because the list is now managed)

Why is this a problem? -[RLMSwiftCollectionBase isEqual:] is currently implemented in a way that it can only ever return YES for unmanaged list objects (see line 89).

This change was introduced by #6845, which attempted to add support for comparing unmanaged Lists and RLMArrays. However, it seems like this PR in fact changed the behaviour so that instead of also being able to compare unmanaged lists, you can now only compare unmanaged lists.

Note: The PR mentioned above also added -[RLMArray isEqual:], with a pretty much identical implementation (only return YES for unmanaged objects).
However, since RLMArray seems to be used exclusively for unmanaged arrays, I left that method unchanged. (RLMManagedArray seems to have a correct isEqual: implementation.)