Most key shortcuts will accept either lower or uppercase ('h' or 'H'),
so we don't strictly match on the shift key, but we prioritize
shifted bindings first, and fallback to unshifted only if no match.
(This lets us differentiate between '←'/'⇧←' or '⌘Z'/'⌘⇧Z')
this should improve compatibility across keyboard layouts (e.g. different languages). Old-style keycodes are still used for browsers that don't implement the new key property.
