Add new descriptions to the `PROP_HIDDEN`, `PROP_SKIP_SAVE`, and
`PROP_LIB_EXCEPTION` flags. For the former two, these are more
explanatory than the previous descriptions. For the latter it's the
first ever description.
Personally I don't think "Do not use ghost values" was particularly
helpful, as the concept of "ghost values" isn't actually that well known
(compared to generally how many people use `bpy`). Granted, it's
described at [1], but IMO if the term "ghost values" is to be kept here,
it should include a link to that page.
[1]: https://docs.blender.org/api/current/bpy.types.bpy_struct.html
Pull Request: https://projects.blender.org/blender/blender/pulls/118036
ff4a473ad4