R1:a8a9fddb0738

Trigger autocomplete when "@" is typed on German keyboards

Summary:
Ref T10252. On the German keyboard layout, you must type "Alt" + "L" to generate an "@" character.

We currently ignore this event, assuming it's a keyboard command. However, I think we can safely continue so that autocomplete works on German layouts.

Test Plan:
- Switched keyboard layout to German.
- Typed Alt + L to generate an "@".
- Typed some username text.
- Got autocompleter.

Reviewers: chad

Reviewed By: chad

Maniphest…