Make disallow-any-unimported flag invertible

[soceanainn]

The --follow-imports=skip CLI option is pretty much unusable in a project where disallow_any_unimported is set to true in the configuration file, as this results in a large number of errors (due to both flags being incompatible). We have a pretty standard project configuration file (with disallow_any_unimported = true and follow_imports = 'normal'), but for specific local development cases where we want to run the mypy CLI with --follow-imports=skip it's incredibly noisy due to the number of errors produced.

This change proposes making the disallow-any-unimported invertible, so that the CLI can be used with --follow-imports=skip in a less noisy way by using:

mypy --follow-imports=skip --allow-any-unimported path/to/my/file.py

[soceanainn]

I moved this down ~20 lines or so, as all invertible flags for this group were defined after non-invertible flags prior to now and I wanted to maintain that convention (assuming this was intentional and not just a coincidence)

[soceanainn]

I'm not fully sure how to test explicitly setting what is already the default behaviour. This test will pass whether or not --allow-any-unimported is set (as long as --disallow-any-unimported is not set).

This is a copy of the test immediately before it. The test before this sets --disallow-any-unimported and asserts that an error occurs, this test sets --allow-any-unimported and asserts no error occurs.

[github-actions]

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

[hauntsaninja]

Thanks! The specific change looks good.

That said, I'm obligated to disclaim that global --follow-imports=skip is evil. It's the most commonly misused mypy config I see. If someone random is reading this, you usually want --disable-error-code import-untyped or maybe --ignore-missing-imports