Implementing workerd::util::Queue<T>

[jasnell]

Scratching a long-time itch... implements a workerd::util::Queue<T> class that wraps std::list with a safer interface. Whereas std::list front() can be called without safety checks when the list is empty, returning a bad reference, the Queue<T> will return a kj::none when the queue is empty. A few other details:

• The queue only permits movable types
• Items can only be appended to the end of the queue
• The traditional iterators are intentionally hidden to limit accidental mutations
• References are not completely hidden or protected (e.g. there's still a peek() method that returns a kj::Maybe<T&> but overall the design should be safer.

This PR converts a number of the existing std::list uses. There are more to do, particularly in api/streams but I'll update those separately.

The whole motivation here is to have a safer-to-use alternative to standard containers.