Vuetify VAutocomplete keydown fires during IME composition

VAutocomplete's keydown listener triggers during IME composition, so confirming a CJK query navigates or selects options.

1. Open a VAutocomplete.
2. Compose a Japanese query, press Enter/arrow to confirm.
3. The keydown listener acts on the composing keys.

Bail out of the keydown listener when e.isComposing is true.