Extend the layout-agnostic handling to the symbol shortcuts. On non-Latin
layouts the characters '/', '?', '#', '!' are often unreachable or on different
keys, so map them from their US-QWERTY physical codes (Slash, shifted Digit1 /
Digit3). Fixes e.g. '?' (open shortcuts help) on a Cyrillic layout.
Shortcuts were matched against event.key, which returns a layout-dependent
character. On non-Latin layouts (Cyrillic, Greek, ...) the physical letter keys
produce non-Latin characters, so single-letter shortcuts (c, j, k, r, e, ...)
never fire and users must switch layout to use them.
Derive the letter from event.code (KeyA..KeyZ) instead, which is
layout-independent. Non-letter keys keep event.key (arrows/Enter are already
layout-independent; #, !, ?, / stay symbol-based).
