Many of the setters are ignored unless others are set - this change:
* Lists these conditions exhaustively.
* Uses more concise language to avoid overshadowing the main details
of what the setter sets.
* Tweaks the language from 'is ignored' to 'shouldn't be called', to
open up the future possibility of throwing an error if these are
called without the 'required' setter also being present (see
Issue: #8957).
#minor-release
PiperOrigin-RevId: 376162385
4033832cba