merge-ort: handle cached rename & trivial resolution interaction better

merge-ort: handle cached rename & trivial resolution interaction better

Back in commit a562d90a350d (merge-ort: fix failing merges in special
corner case, 2025-11-03), we hit a rename assertion due to a trivial
directory resolution affecting the parent of a cached rename.  Since
the path didn't need to be considered, we side-stepped it with

   if (!newinfo)
     continue;

in process_renames().  We have since run into a case in production
where a trivial resolution of a file affects the direct target of a
cached rename rather than a parent directory of it.  Add a testcase
demonstrating this additional case.

Now, if we were to follow the lead of commit a562d90a350d, we could
resolve this alternate case with an extra condition on the above if:

   if (!newinfo || newinfo->merged.clean)
     continue;

However, if we had done that earlier, we would have made 979ee83e8a90
(merge-ort: fix corner case recursive submodule/directory conflict
handling, 2025-12-29) harder to find and fix, and this particular
position for this condition isn't actually at the root of the issue
but downstream from it.

Instead, let's rip out this if-check from a562d90a350d and put in an
alternative that more directly addresses trivially resolved paths that
happen to be cached renames or parent directories thereof, which is a
better fix for the original testcase and which also solves the newly
added testcase as well.

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>