black: merge config into main pyproject.toml now that we have it This means that naive contributors who just run `black` on a source file will get reasonable behavior as long as they have a recent black. Yay! Differential Revision: https://phab.mercurial-scm.org/D9834

#require black test-repo

  $ cd $RUNTESTDIR/..
  $ black --check --diff `hg files 'set:(**.py + grep("^#!.*python")) - mercurial/thirdparty/**'`