convert: update p4 for Python 3 Differential Revision: https://phab.mercurial-scm.org/D10703

tests: change the fixer commands to use the buffer attribute on stdio objects Otherwise `\r` was getting injected into the fixed lines and throwing off the commit hashes on Windows when the fixer is invoked with py3. Differential Revision: https://phab.mercurial-scm.org/D10637

tests: stabilize test-persistent-nodemap.t on Windows Several issues here: - Hooks can't invoke shell scripts on Windows, so use `sh` to launch - `dd` in MSYS only recognizes `status=noxfer` - The `PATH` updating triggered a massive slowdown, but is no longer needed I have no idea why, but removing the `PATH` update substantially increased the speed of the test. It was running finishing at ~4:30 with `--debug` and ~14:50 without it, but now completes in ~2:20 on my Windows laptop. Differential Revision: https://phab.mercurial-scm.org/D10636

tests: invoke some shell scripts through the shell interpreter for Windows Otherwise, Windows was prompting what program to use to open the file (or just opening it if there was a file association configured). Differential Revision: https://phab.mercurial-scm.org/D10635

tests: run python script through quoted interpreter instead of directly This helps Windows when python is installed to %PROGRAMFILES%. Differential Revision: https://phab.mercurial-scm.org/D10634

tests: ensure `$PYTHON` is quoted for Windows Global installs of python3 go into "Program Files", and tons of tests fail with mysterious errors if this isn't quoted. Most of this is a followup to 0826d684a1b5, but a some of these were existing issues. Shebang lines are ignored because quoting breaks direct execution- these will need to be launched indirectly with the quoted `$PYTHON` command. Differential Revision: https://phab.mercurial-scm.org/D10633

black: make codebase compatible with black v21.4b2 and v20.8b1 I don't know what exact version of black made it care about these whitespace differences, but this is the version I got when I just installed it with `pip3 install black`. I'm intentionally not increasing the version of black required, as I don't want to force everyone to upgrade their version of black, and these fixes are backwards compatible with black v20.8b1. If there are more issues in the future and this becomes a maintenance burden I may do so in a future change. Tested with both versions of black (I got the older version via `pip3 install black==20.8b1`) Differential Revision: https://phab.mercurial-scm.org/D10539

debugcommands: fix some plural-agreements I noticed Differential Revision: https://phab.mercurial-scm.org/D10669