py3: introduce pycompat.ziplist as zip is a generator on Python 3
Similar to map, the return value of zip was also turned into a generator on
Python 3. We have multiple occurences in our codebase where we retrieve the
values of zip multiple times, so let's introduce pycompat.ziplist similar to
pycompat.maplist.
Differential Revision: https://phab.mercurial-scm.org/D1675