terminal: improve text pasting
Vte's new vte_terminal_paste_text
lets us do this properly, bringing
pasting inline with g-t
Fix: https://gitlab.gnome.org/ZanderBrown/kgx/-/issues/49
@exalm I suspect this does https://gitlab.gnome.org/ZanderBrown/kgx/-/issues/21 as well, can you check?