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

help: create packages for the help text These files need to be loaded as resources with PyOxidizer, instead of using filesystem representations. AFAICT, the resource loading mechanisms only work for the named package given to it, and can't reach into a subdirectory. While here, the `help` directory is renamed to `helptext`. Without this, trying to load external help text crashed in mercurial/help.py when importing `.i18n`, saying there's no `mercurial.help.i18n` module. Differential Revision: https://phab.mercurial-scm.org/D7376