Merge topic 'ExternalProject-list-separator-docs-example' into release-3.29

5d33f41e23 ExternalProject: reword `LIST_SEPARATOR` to indicate what it *does*
611ffce98c ExternalProject: add an example of `LIST_SEPARATOR` usage

Acked-by: Kitware Robot <kwrobot@kitware.com>
Merge-request: !9376