Since OS X 10.12 it has been named macOS so it makes sense
to reference it in documentation as such, even when it
sometimes refers to older versions which were called (Mac) OS X.
This is a simple high level helper combining an arbitrary control showing
multiple items with the buttons allowing to add items to and remove items from
this control, but using the buttons and the layout appropriate for the current
platform.
Add the implementation itself, an example of using it to the dialogs sample
and the documentation.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@78462 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
