Merge branch 'en/merge-tests'

Preparation for a new merge strategy.

* en/merge-tests:
  t6423: add more details about direct resolution of directories
  t6423: note improved ort handling with untracked files
  t6423, t6436: note improved ort handling with dirty files
  merge tests: expect slight differences in output for recursive vs. ort
  t6423: expect improved conflict markers labels in the ort backend
  t6404, t6423: expect improved rename/delete handling in ort backend
  t6416: correct expectation for rename/rename(1to2) + directory/file
  merge tests: expect improved directory/file conflict handling in ort
  t/: new helper for tests that pass with ort but fail with recursive