Enable newly introduced keys to be used as modifiers

[s1hofmann]

Short overview
We recently introduced new keys (#485), e.g. Key.LeftCmd or Key.LeftWin. These keys are currently not to be used as modifier keys since the lowlevel implementations do not yet know about them being modifiers

[s1hofmann]

Implemented in https://github.com/nut-tree/nut.js/releases/tag/v3.1.2