Bug in Workspaces: Do not allow to publish child elements without selecting the container too, if it is a new container element

[liayn]

Scenario in Core v12:

• User creates a container element and a child element within the workspace
• User publishes only the child element (by accident)
• Live WS shows unused element and ignores the child element (of course)

We should ensure that you can't accidentally publish child elements without their parent container being correctly available.

I did not yet take a look on how this could be fixable (or if possible at all). But at least people that stumble of this behavior may find this report.