Previous comments were rather vague and misleading even. For example it
is often expected that `PROP_HIDDEN` would hide properties in the keymap
editor, which it wouldn't. The term "ghost" value was not defined thus
useless as documentation. Explained the behavior instead.
Also the "Inherits #PROP_SKIP_PRESET" note added in 0d7282e69b was
confusing, what does it mean to inherit a property? Clarified that too.
Lastly the API description of `WM_operator_properties_reset()` was not
updated for 1058006e03. Fixed now.
a1ac565315