This silences binding errors due to keys not found in the current
termcap config in the default fish bindings.
Closes#4188, #4431, and obviates the original fix for #1155
It was necessary to re-implement builtin_bind as a class in order to
avoid passing around the options array from function to function and
as adding an opts parameter to `get_terminfo_sequence` would require
otps to be passed to all other builtin_bind_ functions so they could, in
turn, pass it to `get_terminfo_sequence`.