docs: add typing coverage page #16660
Description
We used to have a page in the documentation about the API stability in different sub-package (until a932250). Maybe we should have an analogous page that would describe to what extent are the different sub-packages typed?
Originally posted by @eerovaher in #16562 (comment)
That sounds good. https://mypy.readthedocs.io/en/stable/command_line.html#report-generation might be good for autodocumenting per-module typing coverage.