Our autodoc_utils Sphinx extension tries to determine some built-in

type mappings to feed to napoleon. In newer versions of Sphinx,

napoleon's mappings get set again in the autodoc's version of the

setting, but too late for us. This ultimately results in our injected

settings always appearing "new" compared to the stored settings for the

doc build, and that forces a full rebuild every time docs are built.
We now set this for both napoleon and autodoc, ensuring this does not

happen.

Successfully built docs incrementally on the versions of Sphinx we test

with.