urlutil: introduce a new `list_paths` function
This function will be useful for command and template that wants to display path
related information.
Differential Revision: https://phab.mercurial-scm.org/D10440
## Avoid interference from actual test env:unset HGTEST_JOBSunset HGTEST_TIMEOUTunset HGTEST_PORTunset HGTEST_SHELL