Device Input System - Step 1

[PolygonalSun]

This PR contains the web implementation for the DeviceInputSystem class. This class will take input from gamepads, mice, and keyboards and allow someone to access (via pollInput) their input values in the same manner.

While it isn't the full version of this system, it's the first step. I'd like to get it checked in so that I can get feedback to create a solid foundation for the next level up on this system.

To use:

Create a variable to hold the device input system and use onDeviceConnected and onDeviceDisconnected to provide custom behavior.

Example:

var dis = new BABYLON.DeviceInputSystem(canvas); // Canvas object needed to attach pointer
dis.onDeviceConnected((deviceName) => {
     if (deviceName == BABYLON.DeviceInputSystem.POINTER_DEVICE)
     {
          scene.onBeforeRenderObservable.add(() => {
               if (deviceName == BABYLON.DeviceInputSystem.POINTER_DEVICE &&
                    dis.pollInput(deviceName, 2))
                    {
                         console.log("Left Click");
                    }
          });
});

Note: This code is not expected to be used by end user but by another system.

[deltakosh]

Pretty cool so far!

[syntheticmagus]

Is there a Playground or something that consumes and tests this? Seems fine enough as an intermediate step, but having some end-to-end, even a hacked-up one, would provide good validation that this does everything it intends to.

[bghgary]

Some nits, otherwise looks good.