simplemerge: make merge_lines() a free function
IMO, the rendering of a conflict as text with merge markers should be
separate from the code for resolving conflicts. The latter is what
`Merge3Text` is mostly about already.
Differential Revision: https://phab.mercurial-scm.org/D11974
[build-system]
requires = ["setuptools", "wheel"]
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
'''
skip-string-normalization = true
quiet = true