Improve cli help somewhat

[wyattscarpenter]

This PR rearranges a couple of command line flag categorizations to make more sense and not leave any uncategorized — which is debatable, if someone really liked how the current top of mypy --help is

options:
  --enable-incomplete-feature {InlineTypedDict,PreciseTupleTypes}
                            Enable support of incomplete/experimental features for early preview

Optional arguments:
  -h, --help                Show this help message and exit
  -v, --verbose             More verbose messages
  -V, --version             Show program's version number and exit
  -O FORMAT, --output FORMAT
                            Set a custom output format

Config file:

instead of

Utility arguments:
  -h, --help                Show this help message and exit
  -v, --verbose             More verbose messages
  -V, --version             Show program's version number and exit
  -O FORMAT, --output FORMAT
                            Set a custom output format (choices: {'json'})

Config file:

This PR also removes the --experimental flag (completing a TODO from 2018-03-16) and programmatically enforces the cli help style guide (from which it removes the advice about links that seemed misguided).

This PR relies on #19062 being merged, as I built off of that to save myself time fixing merge conflict later, and so I'm keeping this as a draft PR for now.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅