This change adds id() property to input_device, which represents the
unique device id. This allows the osd layer when creating a device to
pass a friendly display name along with a unique identifier.
Currently the device id is only used to map a physical controller device
to controller id, but can be used more generally in the future. For raw
input devices, we use the full raw input name as the device id. For all
other devices, we fall back to device name as the device id. The
"uniqueness" of the device id is not currently enforced in code.
This change adds support for configuring device to conrtoller id. This
allows for stable controller ids even if USB devices are plugged /
unplugged, system is rebooted, etc.
See documentation for additional context.
