ISort, various new checks, problem matchers and more - configs

[Jackenmen]

Type

• Bugfix
• Enhancement
• New feature

Description of the changes

List of changes to be completed...

Notes:

• make stylediff reports diffs separately
  • Previously I wrote a tool for running both tools on the files and showing the combined diff
    but I think it's just an unnecessary maintenance burden. Here's a link in case someone is
    interested in this work though:
    563b94a
  • I was also considering removing make stylediff completely since it was primarily added for
    use in CI but it isn't much of a burden to at least keep it in this form and it might be
    useful for some people's workflows. pre-commit usage should, however, be preferred.

TODO:

• re-enable flake8 for tests/ after figuring out a proper way to minimize the issues with the imports
• Incorporate pylint too? Maybe it would be better as separate PR once pylint 2.7.3 gets released; TBD
• Add a new recipe to Makefile that creates a new venv and auto-installs pre-commit as part of it
  • basically make newenv + pre-commit install combined
  • alternatively, we could just print a message in make newenv after it finishes everything else
• add the following commits from ISort, various new checks, problem matchers and more - reformat #4894 once it's merged:
  • "Address issues from flake8"
  • "Reformat with Black 22.1.0"
  • "Reformat with isort 5.10.1"
  • "Remove trailing whitespace"
  • "Make files end with one empty line"
  • "Reformat JSON files with pretty-format-json hook"

Things that I have considered but ended up not doing:

• a Makefile recipe that calls pre-commit run --all-files
  • note: this would have been a single recipe and it would not be the same as reformat, stylecheck, or stylediff as not all hooks are able to automatically reformat the files
  • I think that there isn't much use for this, pre-commit works better as
    an installed pre-commit hook, it already runs in CI, and it isn't particularly
    hard for people to run pre-commit run --all-files if that's their preferred workflow
• auto-install pre-commit as part of newenv recipe in Makefile
  • it is not a good idea to force this workflow on people

The reformatting needed by this PR is done in #4894 and that PR should be merged before this one.

Link to problem matcher preview: 6378fdf (can also be seen on the "Files changes" page in "Unchanged files with check annotations" section)

Fixes #3882, fixes #4698

Blocked by #4894 (the one that actually does the reformatting)