Replaced Ord by TotalOrd in priority queue
Rename to_vec and to_sorted_vec
Refactored and renamed functions to avoid failure
Fix dead code warnings
Fix insert_ordered in DList
auto merge of #14279 : aochagavia/rust/pr2, r=huonw

The breaking changes are:

* Changed `DList::insert_ordered` to use `TotalOrd`, not `Ord`
* Changed `PriorityQueue` to use `TotalOrd`, not `Ord`
* Deprecated `PriorityQueue::maybe_top()` (renamed to replace `PriorityQueue::top()`)
* Deprecated `PriorityQueue::maybe_pop()` (renamed to replace `PriorityQueue::pop()`)
* Deprecated `PriorityQueue::to_vec()` (renamed to `PriorityQueue::into_vec()`)
* Deprecated `PriorityQueue::to_sorted_vec()` (renamed to `PriorityQueue::into_sorted_vec()`)
* Changed `PriorityQueue::replace(...)` to return an `Option<T>` instead of failing when the queue is empty.


[breaking-change]