Fix EditorInterface.get_selected_paths() working incorrectly when FileSystemDock is in split mode

[fstxz]

Fixes #88228

[AThousandShips]

Will try and test this tomorrow

[fstxz]

I wonder if folders that are selected in the tree should also be included when in split mode? Otherwise you can't select multiple folders that are in different places without changing the display mode to tree only.

[AThousandShips]

I've confirmed the bug and confirmed that this PR works correctly in both modes (i.e. doesn't regress with the single tree mode selected)

I'd say the expected behavior is that the list of files is returned, but the option of including the folder as well might be considered, though I think we can go with this and see what we might want later as well (we could add a note to the documentation clarifying what exactly is returned, elaborating that it returns just the files selected in split mode)

Approving on that this works and the code looks good, might be a more elegant solution but I'm not familiar with the code here so can't speak to that

[KoBeWi]

In split mode if you have a folder selected, but none of the files, the returned list is empty. If no file is selected, maybe the selected directory should be returned at least?

[fstxz]

@KoBeWi I updated the PR, I hope this is what you meant.

[KoBeWi]

Seems like it's possible to multi-select in tree in split view, so maybe all selected directories should be returned 🤔
But this way it's fine too.

[fstxz]

Seems like it's possible to multi-select in tree in split view

It's also possible to deselect everything with ctrl, this is why I chose to return ony the current directory.

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉

[akien-mga]

Cherry-picked for 4.3.1.