utils: move finddirs() to pathutil...
utils: move finddirs() to pathutil
This is a follow-up to
c21aca51b392 (utils: move the `dirs` definition
in pathutil (API), 2019-11-06). finddirs() is closely related to dirs
and used by it.
Differential Revision:
https://phab.mercurial-scm.org/D7388