Fix exit shortcuts for non QWERTY keyboards

[germain-gg]

Fixes element-hq/element-web#16938

I was unfortunately using KeyboardEvent.code. When reading through the MDN documentation there is a fair warning saying

Warning: This ignores the user's keyboard layout, so that if the user presses the key at the "Y" position in a QWERTY keyboard layout (near the middle of the row above the home row), this will always return "KeyY", even if the user has a QWERTZ keyboard (which would mean the user expects a "Z" and all the other properties would indicate a "Z") or a Dvorak keyboard layout (where the user would expect an "F").