path: add a new argument to control path validation
During pull, unvalidated path might be used, having the option to do so directly will allow use to simplify some code and unlock more `path` usage later in the series.
Differential Revision: https://phab.mercurial-scm.org/D11671
edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true