I'd messed up a rebase in my previous iteration, causing `weakly_canonical` to reappear,
but not trigger a test failure.
These two functions behave similarly when the argument is a path that points to a broken
symlink. `weakly_canonical` would not resolve it because the target doesn't exist, and
`makeParentCanonical` would not resolve it, because it never resolves the final path
element.
This new test case now also tests a valid symlink, "differentiating" the two.
(cherry picked from commit 4c74d679b6)
336fdaa119