Keymap.addVirtualModifiers

Maps the non-virtual modifiers (i.e Mod2, Mod3, ...) which are set in state to the virtual modifiers (i.e. Super, Hyper and Meta) and set the corresponding bits in state.

GDK already does this before delivering key events, but for compatibility reasons, it only sets the first virtual modifier it finds, whereas this function sets all matching virtual modifiers.

This function is useful when matching key events against accelerators.