Merge branch 'en/ort-rename-fixes' into maint-2.51

Merge branch 'en/ort-rename-fixes' into maint-2.51

Various bugs about rename handling in "ort" merge strategy have
been fixed.

* en/ort-rename-fixes:
  merge-ort: fix directory rename on top of source of other rename/delete
  merge-ort: fix incorrect file handling
  merge-ort: clarify the interning of strings in opt->priv->path
  t6423: fix missed staging of file in testcases 12i,12j,12k
  t6423: document two bugs with rename-to-self testcases
  merge-ort: drop unnecessary temporary in check_for_directory_rename()
  merge-ort: update comments to modern testfile location