Bug 1654103: Standardize on Black for Python code in `mozilla-central`....

Bug 1654103: Standardize on Black for Python code in `mozilla-central`. r=remote-protocol-reviewers,marionette-reviewers,webdriver-reviewers,perftest-reviewers,devtools-backward-compat-reviewers,jgilbert,preferences-reviewers,sylvestre,maja_zf,webcompat-reviewers,denschub,ntim,whimboo,sparky

Allow-list all Python code in tree for use with the black linter, and re-format all code in-tree accordingly.

To produce this patch I did all of the following:

1. Make changes to tools/lint/black.yml to remove include: stanza and update list of source extensions.

2. Run ./mach lint --linter black --fix

3. Make some ad-hoc manual updates to python/mozbuild/mozbuild/test/configure/test_configure.py -- it has some hard-coded line numbers that the reformat breaks.

4. Make some ad-hoc manual updates to `testing/marionette/client/setup.py`, `testing/marionette/harness/setup.py`, and `testing/firefox-ui/harness/setup.py`, which have hard-coded regexes that break after the reformat.

5. Add a set of exclusions to black.yml. These will be deleted in a follow-up bug (1672023).

# ignore-this-changeset

Differential Revision: https://phabricator.services.mozilla.com/D94045