Pop on binary heaps does not have constant time complexity.

pop calls siftdown, siftdown calls siftdown_range, and siftdown_range
loops on an index that can start as low as 0 and approximately doubles
each iteration.
auto merge of #19450 : jbapple/rust/pq-pop-time, r=Gankro

pop calls siftdown, siftdown calls siftdown_range, and siftdown_range
loops on an index that can start as low as 0 and approximately doubles
each iteration.