Terminal editors: splitted terminal is not preserved as terminal editor

[weinand]

Testing #127192

• in a panel split a terminal
• shift select the two terminal tabs that comprise the spitted terminal
• drag them to the editor group

Observe:
there is no longer a splitted terminal. Instead both halves show up as individual terminal editors

[Tyriar]

This is actually by design and I think trying to do this would end up leading to some weird behavior as well, like when dragging from multiple groups.