gamepad support for winit using gilrs

[Calcoph]

Have to use WinitPlatform::handle_controller_event() instead of WinitPlatform::handle_event()

Adds the dependency gilrs to imgui-winit-support

[sanbox-irl]

hi @Calcoph thanks for the hard work!

However, i feel uncertain about this PR and think it might be best to close it for now. That's because this actually can be entirely handled by users directly rather than baked into this crate -- IMO that's a big win. In fact, i really see your work as having two distinct halves -- an imgui-gilrs crate, which handles imgui + gilrs type glue, and your hook into winit. I'd love to support such an imgui-gilrs crate with a shoutout on the README, but this repository has made many errors by overly directly supporting many third party dependencies. This hasn't been a great idea, so I'm loathe to take on another dependency whose updates we'd need to follow.

[Calcoph]

I like your idea of a separate imgui-gilrs crate, since it doesn't really need any of the private imgui-winit-support code. In order to not put extra pressure onto imgui mantainers, I've decided to make that crate separately. It's here if anyone is interested.

[sanbox-irl]

Thank you! I'll add a line in the README for this project