Mac Alt+_ shortcuts don't work

[luca3s]

On mac the shortcuts using alt only work if the menu bar item they are in is selected. This is probably due to macos translating a lot of alt combinations into weird characters (see also helix-editor/helix#2280 (comment)).

From short experimentation with winit it reports "key_without_modifiers" as a platform specific extentions to the KeyEvent struct. Keyboard shortcut testing should probably be done against that.

https://docs.rs/winit/latest/x86_64-apple-darwin/winit/platform/modifier_supplement/trait.KeyEventExtModifierSupplement.html

cc @timon-schelling