Add __reversed__ method to FrozenBitsets

[trevorkarn]

One can currently iterate over the elements of a FrozenBitset, but only in the forward direction. This ticket fixes that.

CC: @tscrim @jasongrout

Component: misc

Keywords: gsoc2022 frozenbitset iteration reversed

Author: Trevor K. Karn

Branch/Commit: d4f3d86

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/34035

[trevorkarn]

comment:2

cc'ing Jason as original author.

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:3

This will work for now, although both this and the iterator would be better to not create the whole list and then iterate over it (more important for large bitsets). Although for the reversed, this would be much harder to do than the forward iterator.

[vbraun]

Changed branch from u/tkarn/reverse-frozenbitset to d4f3d86