* Make sidebar nav in language docs more intuitive
* Minor display fixes for registry docs
* Explain providers in the registry in the providers index
* Revise a bunch of language docs around provider reqs
This is mostly an effort to smooth out some of the explanations, make sure
things are presented in a helpful order, make sure terminology lines up, draw
connections between related concepts, make default behavior more apparent, and
the like. It shouldn't include very much new information, but there might be one
or two things that came out of a conversation somewhere.
Co-authored-by: Judith Malnick <judith@hashicorp.com>