Although I hoped we could keep the non-ascii alt characters, it turns
out this is not the case for all keyboards.
Fixes #21175
Release Notes:
- (breaking change) editor::ShowInlineCompetion is now `option-tab` on
macOS
(not `option-/`). editor::{Next,Previous}Completion are `option-tab` and
`option-shift-tab` (not `option-[` and `option-]`). This fixes typing
characters generated by option-{/,[,]} on keyboards like Croatian.