Migrate typing documentation to `pyproject.toml`

[konstin]

Documentation

The official typing documentation recommends using a setup.py without pyproject.toml (https://typing.python.org/en/latest/guides/libraries.html#companion-type-stub-package, Doc/library/typing.rst). This relies on pre-PEP 621 fallback behavior, while we should teach users to follow PEP 621 and use pyproject.toml. Can we migrate this documentation to use pyproject.toml, including [project] and build-system] as well as [tool.*] for configuration?

The documentation at from packaging.python.org has a tab selection for different build backends, with a default of hatchling instead of setuptools (https://packaging.python.org/en/latest/tutorials/packaging-projects/#choosing-a-build-backend). We found that this is easier to work with than setuptools. A possible alternative would be having the same tabs on typing.python.org (I don't know if that's supported in the renderer), or to move the packaging part of the documentation to packaging.python.org.

[srittau]

It makes sense to me to modernize the instructions to use pyproject.toml.

[Josverl]

Yes makes perfect sense.
I have a personal preference not to use setup.py, and still remember needing to quite a bit of searching and trail and error before getting it right.

Having samples for a few different backends will help clarify what to configure where.
I would suggest a few useful options such as :

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

[tool.hatch.build.targets.wheel]
only-include = ["foo", "bar"]
exclude = ["*.py"]