DOC: New round of NEP 42 edits (gh-17493)
DOC: New round of NEP 42 edits (gh-17493)

* DOC: Revise NEP 42 "common DType" section

* DOC: Eliminate duplicate doc in NEP42

* DOC: Fix missing 'not' in NEP42 edit

* DOC: Minor typos in NEP42 edit

* DOC: Reword opening sentence of NEP 42 revision

Also clarify a wording.

* DOC: Correct :class: reference in NEP42 edit

* DOC: Fix Windows line-enders on NEP42 edit

* DOC: New round of common DType edits of NEP 42

* DOC: Uniquify anchors in NEP 42

* DOC: Typo in NEP42 edit

* DOC: Last push for NEP 42 edit

* Small fixups and moving example

One paragraph on `__common_dtype` in the alternatives was already
before very confusing. This makes it hopefully more clear.

* NEP: Change title to "New and extensible DTypes"

Co-authored-by: Sebastian Berg <db043b2055cb3a47b2eb0b5aebf4e114a8c24a5a@sipsolutions.net>
pdebuyl/numpy,simongibbons/numpy,jakirkham/numpy,rgommers/numpy,charris/numpy,numpy/numpy,pbrod/numpy,simongibbons/numpy,charris/numpy,seberg/numpy,grlee77/numpy,madphysicist/numpy,mhvk/numpy,endolith/numpy,rgommers/numpy,mhvk/numpy,jakirkham/numpy,grlee77/numpy,charris/numpy,madphysicist/numpy,anntzer/numpy,mhvk/numpy,seberg/numpy,jakirkham/numpy,grlee77/numpy,endolith/numpy,endolith/numpy,mhvk/numpy,anntzer/numpy,mattip/numpy,simongibbons/numpy,simongibbons/numpy,jakirkham/numpy,seberg/numpy,numpy/numpy,pdebuyl/numpy,grlee77/numpy,rgommers/numpy,mhvk/numpy,madphysicist/numpy,grlee77/numpy,anntzer/numpy,pbrod/numpy,simongibbons/numpy,pbrod/numpy,rgommers/numpy,pdebuyl/numpy,pdebuyl/numpy,madphysicist/numpy,numpy/numpy,jakirkham/numpy,pbrod/numpy,anntzer/numpy,endolith/numpy,pbrod/numpy,mattip/numpy,charris/numpy,mattip/numpy,mattip/numpy,seberg/numpy,numpy/numpy,madphysicist/numpy