`InputMap::ALL_DEVICES` and `InputEvent::DEVICE_ID_EMULATION` have the
same value `-1`.
Change value of `InputMap::All_DEVICES` so that it's different from
`InputEvent::DEVICE_ID_EMULATION`. `InputEvent::DEVICE_ID_EMULATION`
is part of the API and can't be changed without potentially breaking
projects.
Gather all special device constants in a single location inside
`InputEvent`.
Add a converter to project settings, that takes care of adjusting
project files during loading.
916d480686