Silence bind errors in default key bindings

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`.

share/functions/fish_default_key_bindings.fish

@@ -18,6 +18,11 @@ function fish_default_key_bindings -d "Default (Emacs-like) key bindings for fis
         end
     end
 
+    # Silence warnings about unavailable keys. See #4431, 4188
+    if not contains -- -s $argv
+        set argv "-s" $argv
+    end
+
     # These are shell-specific bindings that we share with vi mode.
     __fish_shared_key_bindings $argv
     or return # protect against invalid $argv