Teensyduino joystick support

Feature Request

Generic controllers (like the Teensyduino Joystick) are not registering in Proton, they do work if I enable Steam input but then suffer from major dead zone issues not really favorable in simulations.

I confirm:

• that I haven't found another request for this feature.
• that I have checked whether there are updates for my system available that
  contain this feature already.

Description

I would like to see generic joystick support, if you own a Teensy you can check my git repos for the SBUS joystick and test with that.

Justification [optional]

It is game related, for example the game Skater XL has a mod to fly a quadcopter and I would like to use my transmitter as a joystick. My XboxOne controllers work no problem, only the generic and DIY joysticks register zero inputs.

GTA V has a similar mod, I could get that to work with some trickery but also stumbled on the dead zone issues.

Start by locating Proton's generic joystick input handling and reproduce the issue with a Teensyduino or SBUS joystick, comparing it with the working Xbox One controller and the Steam Input path. Done means generic and DIY joystick inputs register in the affected games without the reported dead-zone problems.