The files and commit files panels each had their own copy of this, one of
which used to be missing the previous path of a rename. Growing them
apart again is the last thing we want, since the next commit needs to
teach both of them about renames that cross a directory boundary.
The files panel version only returned paths for the filtered case, and
left it to WorktreeFileDiffCmdObj to derive the rest from the node; now
that all callers pass the paths in, that command doesn't need to know
about renames at all.
