If you're using the old binding that only clears the commandline and
doesn't preserve its contents and start a new line, you can use
```fish
bind \cc "commandline -f cancel; commandline ''"
```
instead.
Closes#4298.
This didn't work on platforms where tput exists but can never accept
terminfo names. This includes the current versions of FreeBSD - it
used to do both, now it doesn't. So, fall back to the old termcap names
by (tput smso; or tput so). Add check for the tput program before we
even try.
There was an extended discussion in https://github.com/fish-shell/fish-shell/issues/2904 about using a bright yellow background to make the cancelled command indicator, ^C, standout. The upshot was that standout (i.e., reversing fg/bg colors) mode should be used until themes are agumented with proper support for background colors and special characters.
