merge: add commands.merge.require-rev to require an argument to hg merge
This is related to commands.rebase.requiredest, commands.update.requiredest, and
commands.push.require-revs. Since it isn't really a "destination", I went with
require-rev to be similar to push's require-revs.
Differential Revision: https://phab.mercurial-scm.org/D7620
[tool.black]
line-length = 80
exclude = '''
build/
| wheelhouse/
| dist/
| packages/
| \.hg/
| \.mypy_cache/
| \.venv/
| mercurial/thirdparty/
| contrib/python-zstandard/
'''
skip-string-normalization = true
quiet = true