basic/terminal-util: add code to read window size using CSI 18

basic/terminal-util: add code to read window size using CSI 18

In my tests, the sequence works on Ptyxis 49.0, gnome-terminal-3.56.3,
xterm-401, rxvt-unicode-9.31, under tmux-3.5a, over ssh and serial console
connected to ptyxis. It did not work on a text console in a VM (TERM=linux) or
under kmscon-9.1.0 (TERM=vt102).