Run black on all files previously linted by autopep8, excluding "contrib" (will be split over more diffs for ease of review).
See D13876 for more background on black.
Note that this also touches some files previously processed in D13879, D13880 and D13881. This is because I did not rerun the linter after landing D13882, so already submitted diffs did not apply a few of the --preview related changes.
Depends on D13888