doc: clarify napi_property_attributes text

* Rearrange sentence to avoid ambiguity whether the entire sentence
  applies to a method in a JS class or just the "but not" part
* Use serial comma
* Correct spelling of _configurable_

PR-URL: https://github.com/nodejs/node/pull/35253


Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Michael Dawson <midawson@redhat.com>
Reviewed-By: Gerhard Stöbich <deb2001-github@yahoo.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>