`Heap` should have a `removeAll(where:)` method

[lorentey]

Heap is intentionally not a Collection, but it should still provide an (O(n)) removeAll(where:) method for filtering out unwanted items.

[DakshinD]

Saw this old issue, I would be interested in implementing this as my first contribution to the repo.

A straightforward implementation would be filtering the underlying storage buffer in O(n) and then using heapify to construct the heap again in O(n). Any input as to faster approaches?