[editor] Fix undefined results with unbound keys in viins/vicmd
[editor] Fix undefined results with unbound keys in viins/vicmd

Bind the remaining unbound keys in the main mode so that they
don't result in undefined functionality when pressed. (Often this
will change the casing of one/most/all of the characters you've
typed or even stranger things). In emacs mode this usually just
inserts a tilde, but this will fix that as well so nothing happens
when unbound keys are pressed.

Since there isn't any binding which does "nothing", create a noop
ZLE widget and bind them to that.

The user or other modules are still able to override these bindings
either by overriding the main keymap or setting a keymap in one
of the other modes which will take precedence over the main fallback.

ysfjwd/prezto