Add xdg-terminal-exec to terminal search list

This gives people a way to use their preferred terminal when launching
"Open in Terminal" applications, by making use of xdg-terminal-exec,
from https://github.com/Vladimir-csp/xdg-terminal-exec/.
9 jobs for add_xdg-terminal-exec in 17 minutes and 1 second (queued for 3 seconds)
latest