We cannot just use TERM = xterm and defined Ss sequence, as some old
vte-based terminals are still in the wild that don't support the
sequence and don't have $VTE_VERSION set.
I have tested this on
- konsole - supported and works ($KONSOLE_PROFILE_NAME)
- new xterm - supported and works ($XTERM_VERSION)
- lxterminal-gtk3 - supported and works ($VTE_VERSION)
- new gnome-terminal - supported and works ($VTE_VERSION)
- lxterminal-gtk2 - not supported and deactivated (no $VTE_VERSION)
- tmux in konsole - works
- tmux in lxterminal-gtk2 - deactivated
and for all supported ones with the respective variable erased, to see
that it is deactivated.