copilot: Propagate action if suggest_next is not possible. (#3129)

One of our users ran into an issue where typing "true quote" characters
(option-[ for „ and option-] for ‚) was not possible; I've narrowed it
down to a collision with Copilot's NextSuggestion and PreviousSuggestion
action default keybinds. I explicitly did not want to alter the key
bindings, so I've went with a more neutral fix - one that propagates the
keystroke if there's no Copilot action to be taken (user is not using
Copilot etc). Note however that typing true quotes while using a Copilot
is still not possible, as for that we'd have to change a keybind.

Fixes zed-industries/community#2072


Release Notes:
- Fixed Copilot's "Suggest next" and "Suggest previous" actions
colliding with true quotes key bindings (`option-[` and `option-]`). The
keystrokes are now propagated if there's no Copilot action to be taken
at cursor's position.