[input] Only load terminfo feature of zsh/terminfo
[input] Only load terminfo feature of zsh/terminfo

and use `-F` to check if the feature was not already loaded before.

Use terminfo elements for Backspace and Delete. Sort by terminfo element
keys.

Also simplify code, removing unnecessary double quotes, and replacing
if-then-fi with one command by one-liners.

joshuarubin/dotfiles,joshuarubin/dotfiles,joshuarubin/dotfiles,Eriner/zim,joshuarubin/dotfiles