Replace class with AnyObject in all protocol definitions

[tbarbugli]

What do you want to happen?

Replace class with AnyObject in all protocol definitions (class is deprecated). Happy to do it myself unless there is a reason not to make this change.

public protocol EngineDelegate: class {

into

public protocol EngineDelegate: AnyObject {

[odrobnik]

👍

This produces a deprecation warning on Xcode 13.

Using 'class' keyword to define a class-constrained protocol is deprecated; use 'AnyObject' instead

[kohenkatz]

It looks like this was already fixed in #894 but there hasn't been a tagged release in a very long time.