There is no natural default binding for token movements. Add the
alt-{left,right,backspace,delete}, breaking some existing behavior.
For example, backward-delete-word is no longer bound to alt-backspace but
only to ctrl-backspace. Unfortunately some terminals (particularly tmux)
don't support distinguishing ctrl-backspace from ctrl-h yet, so the loss
of alt-backspace may be tragic.
---
I guess we could also add:
bind alt-B backward-token
bind alt-F forward-token
bind ctrl-W backward-kill-token
bind alt-D kill-token
Those might be intercepted by the terminal on Linux, but I don't know where
that happens.
Tested on foot, kitty, alacritty, xterm, tmux, konsole and gnome-terminal.
Closes#10766
