toolbar/terminal: Open in selected sub-folder, in expanded list-view

[gkatev]

Hi,

In the list view, you can expand folders to view their content without actually navigating into them, potentially multiple levels deep at once. The Open Terminal in the active folder button on the toolbar does not work well in such situations, as it always opens the terminal in the top/root folder, even if a folder deep down in the expanded hierarchy is selected.

This PR proposes/implements a change in this behaviour, making the terminal toolbar button work the same way as the Create a new folder button, which does take into account the currently selected folder in the hierarchy.

• If no folder is selected, opens terminal in the top-most folder.
• If a non-expanded folder or a file is selected, opens terminal in its parent's directory.
• If an expanded folder is selected, opens terminal in the selected folder.

I was inspired to use nemo_view_get_backing_uri() from nemo_view_new_folder(). Tested on 6.4.5.